If you only do that, though, you are being immature and kind of a dick. I used to think "if someone is bothered by this and there's no good reason to be bothered, fuck them" , but that's selfish and small minded and just douchey. If you know people will be bothered - and it's somewhat reasonable for them to be bothered - even if they aren't significantly hurt by it, then you should adjust your actions. For example, talking loudly in a museum doesn't really hurt anyone, it's not like we're fucking art scholars concentrating so hard on the paintings that we need absolute silence, but it's still douchey. On the other hand, talking loudly at a restaurant is perfectly fine, and if stuffy fuddy duddy mc-fuck-pants gives you a dirty look from the next table over, fuck him, he's applying an overly restrictive behavior code that you can reject.
Anyway - where does the car pool lane cheat fall in this spectrum ? I believe that it basically doesn't hurt anyone. Silly people might argue "if everyone cheated in the carpool lane it would ruin the whole purpose of the carpool lane". That's wrong on two points - 1. the carpool lane basically has no purpose to begin with; there is no strong data showing that they actually help traffic or reduce car use significantly, and 2. it's not a problem that's in danger of becoming endemic, since ticket enforcement makes it too expensive for most. Assuming you get a random occasional ticket, it's basically a toll lane to let the rich go faster, which is a perfectly reasonable thing. (Some are opposed to this kind of thing due to some misplaced egalitarian principle, the belief that rich should not have better access to services than ther poor; that is naive and just retarded. The rich will always have been services than the poor, what you should instead fight for is fairness on two fronts : 1. make sure the rich actually pay a fair price for their improved services (currently they often do not), and 2. make sure the poor have the opportunities to become rich (currently they certainly do not)).
Logically all arguments tell me I should be cheating in the car pool lane, but when the moment comes to do it, I just can't make myself. It's partly the thought of all the other cars looking over at me thinking "that fucking douche" ; I wish I could ignore that, but it does bother me. It's also the memory of all the many times I myself have looked over at carpool cheaters and thought "that fucking douche" , and I want to be in that morally superior condescending group - but of course that's just retarded self-defeating martyrdom.
ADDENDUM : Okay, I got some more info ; contrary to what certain people believe, an HOV Lane violation *is* a moving violation in WA (and in most states actually). Some insurance companies apparently do not count it against you, but some do. Apparently it's pretty easy for a lawyer to get it changed to a non-moving violation like "careless driving" (it boggles my mind that "careless driving" would not be a moving violation and not affect your insurance, but there you go). So that is a bit of a real reason to not cheat. Some states have a strict "point system" for licenses, in which case an HOV violation would either be a point or not, but WA does not have legally detailed points, rather they just report all moving violations to the insurers and let them decide how your rate should be set. Because of that it's rather hard to get solid information about what affect exactly an HOV violation or a bicycling violation or whatever would do to your rates.