I use mine at 40% brightness as well, perfect spot. The only thing the people I showed it off to weren't impressed with the camera quality, but they were blown away by the no shutter lag, got about 50 or so pictures of the same thing cause of no shutter lagI use mine at 40% brightness, seems to be the best spot for me without destroying the battery.
My colors are pretty amazing, was at a playoff party this weekend and I couldn't get my phone away from friends wanting to check the screen out.
Even had a girl with a 4S say she thought the screen looked better than hers, was a good night=P