The car doesn't really like to be cold. For one thing it's sold on "summer tires", and below 45 F or so you really need to be on "winter tires". (winter tires does not mean "snow tires" ; the difference between summer and winter tires is the rubber compound; you want tire rubber to have just the right softness in the operating temperature range; winter tires are chemically created to be soft at low temperature, but you can't use them year round because they would get too soft in heat; there's also a difference in the depth and style of tread, but the rubber compound is the bigger issue; summer tires become hard like plastic below 40 F). But even beyond that, the engine is designed to be track friendly, which means its operating temperature range is very high. It's hard to make an engine that works well both at very low and very high temperatures; one issue is the motor oil in the engine; no oil can handle a temperature range from 0 F (cold winter start) all the way up to 300 F (heavy track use). Track racers use 15W50 , winter street users use 0W40 ; the engine's not really happy until it's over at least 175 F. This means if you want to go racing in the winter you need to warm it up a long while (5-10 minutes ; just watch your oil temp gauge).
Some Porsche engines eat oil, some don't. It's sort of a random chance whether you get an oil eater or not. Not really a huge deal either way, it just means adding a liter or two between oil changes (oh, BTW, the manufacurer recommended 10k or 15k miles between oil changes is bullshit - it's part of what causes blown engines; use 5k intervals!). What *is* annoying is the fucking electronic oil measurement. It refuses to give a reading unless the oil has descended into the oil pan, so you can't do it when the engine has been run at all, you have to let the car sit for 10-30 minutes to get a reading. But you also don't get an accurate reading if the car has sat for a long time, so you can't just do it in the morning after the car sits overnight. Also the car has to be level to get a reading. Very annoying. Each electronic oil tick is half a quart. You should try to keep it between the bottom and middle tick mark - not at the top, keeping it fully topped up will encourage it to burn oil faster. (Porsche officially says that burning up to 1 quart per 400 miles is "by design" ; most cars, like mine, seem to burn about 1 quart per few thousand or so, while a few cars don't burn any at all).
The rear parking sensor thing beeps. It's a bit annoying because it starts beeping when you are like 10 feet away from the thing behind you. I'm always like "really? you're beeping already?". I just discovered recently that it will actually go to a solid tone after beeping and you still have about 6 inches behind you at that point. The parking sensor also can't detect thin or very low objects, so it's better to just use your eyes and ignore it (preferrably buy a car without that option).
The PCM computer thing is really awful for playing music. It does play MP3 CD's and it recognizes the directory structure and will show you folder names, that is handy. There is NO aux input for ipods or whatever. That is fucking retarded. You can get an aftermarket kit to plug in your ipod for $500 or so. The PCM audio can't do simple things like turn off the radio but leave the CD player on (eg. when you eject CDs it starts playing radio). You can't turn on & off the audio separately from the Nav/etc. It also can't pause CDs from the normal controls; I just discovered the other day that you can in fact pause CDs from the multi-function steering wheel by pressing on the volume wheel.
The Bose stereo is pretty fucked up; first of all you must turn off the "adaptive surround" or whatever it's called where they try to create surround sound from stereo. Then you have to tweak all the treble and bass settings drastically to try to get something decent out of it. One quirk is that there are separate settings for FM and CD mode, so you have to be playing in that mode to tweak it, and you have to do all the tweaks twice.
The rear subwoofer and the rear seats are both easily removed if you want to save weight for track days or make more room for cargo or whatever.
The default alignment on the car is very "mild" ; that is, it's very stable, keeps the car straight on the freeway when you let go of the wheel, and resists turning, making the car understeer slightly. This is nice for highway driving and many people will be happy with it. If you want more aggressive turn-in, the easiest way to fix that is just to get a more aggressive alignment; the biggest difference comes from getting more negative camber up front, but you can also get less toe in. You can just ask for the "rest of world performance alignment".
Something about the front alignment (maybe it's the caster ?) means that when you turn all the way to lock, you actually are up on the edges of the tire. Obviously you don't have great control when you're on the edges of the tire and it can feel squirelly, especially if the tires are cold and stiff. They can "scrub" or "crab" and make some crunchy sounds. It's not bad once the tires are warm, but you still probably shouldn't slam on the gas at full lock. It's not a great car for gymkana unless you do some suspension mods. (BTW getting a "performance alignment", as you should do, will mostly fix this)
It's hard to get the transmission back into 1st gear once you've been up to high speeds (after you slow back down). You can solve this by double clutching : put it in neutral, let out the clutch, put the clutch back in, put it in 1st. This is "by design" ; many Porsche drivers just keep the car in 2nd once it gets moving. You can't really use 1st gear once you get moving, which sort of sucks for low speed corners (such as in autocross) because you get into super low revs in 2nd gear.
Almost every part of the car is just held together by little plastic tabs, you know those bits that click together. This is kind of handy because it means everything is very easy to take apart and put back together, but it also means that it's not super solid feeling. The cabin has a lot of squeaks and rattles. You can fix these pretty easily by just popping out the offending piece, putting a bit of foam or felt tape under it and popping it back in. But trying to do that on every piece would drive you mad.
I often think that there's some horrible rattle from a loose piece of the car. In fact every time it has just been something I put in the car, a key chain, a quarter in the change tray, etc. The car gets a lot of vibration from the road because the suspension is pretty stiff, so anything you carry in the car will bounce around quite a lot.
The electricity is on inside the car all the time, even when it's shut off and the doors are locked. This means your cabin accessories plugged into the various 12V DC ports will stay on. Personally I find that annoying, others may like it. It also means the car will drain the battery if it sits a while; people who keep their Porsches in garages all the time usually have to buy a battery tender.
If the battery goes completely dead it's a pain to deal with cuz the hood is power operated. You have to first put jumpers on the fuse panel in the driver's footwell, then use the hood open switch on the key, not the one in the car. (there is also an emergency manual hood open wire, but it requires taking apart the right wheel well, so the fuse panel method is preferred when possible)
Like most cars these days, you can disable the seatbelt warning chime by plugging the seat belt in and out 15 times quickly (this makes the computer think it's broken and thus disabled it). Or you can buy a Durametric (Professional) cable that will let you toggle all the option codes in the chip the way a dealer can. (it's OBDII which I guess is a standard interface that lots of cars are on these days, you can get a generic OBDII device for cheap that can at least read engine failure codes and clear service lights, but you can't toggle options with a generic device).
The Porsche as a daily driver is mostly great. The main problem with it is not the harsh ride or the low cargo space, it's that it wants you to really drive it. It begs you to hammer the throttle and swing through the curves. That's great, right? Well mostly yes, but not always. Some days you just want to turn off your brain for the commute and get to work without incident. Some days it's easier to deal with the traffic and annoyance if you have a sedative in the form of a non-performant car. I found that when I was driving the Nissan Versa rental car - you can't go fast even if you want to, and that actually is very relaxing. The Porsche is like a girlfriend who wants to have nasty hard sex every day. Sounds great, right? Well, after the 20th day in a row of fucking, you kind of just want to watch TV and be left alone, but she's still jumping on you and whipping you with her hair; at that moment you kind of wish you had a fat lazy girlfriend who just eat chips with you and sits on the couch.