More importantly, it's a HUGE perf dog. It seems to be hitting the monitor settings something like once a second. I was testing the framerate in some of my apps and noticed a weird spiking of long frame times once a second (my new Thread Profiler tracks frame times and shows you a nice graph of the frame durations over time so you can see how your framerate is varying and pick out long frames and such). With f.lux installed there's a huge hitch of 100 millis or so once a second. Yikes. Uninstall.
I also find the cutesy UI moderately annoying. The visual appearance of the UI is very nice, but the way everything fades in and out is just a waste of my time. When I click buttons I want the mode to change *NOW*. When I close a window I want it to be gone immediately. I hate apps that skin themselves in weird custom ways. Just use the damn standard Win32 UI peoples.
Anyway, the basic idea is good, so I'm putting it on my todo list to write my own.