The first thing I noticed about commuting on a bike was an attitude change. Instead of wanting to strangle every other driver, I was at peace, at one with the world - and the force was with me. The next thing I noticed about attitude was after I had my first accident this year and had to take some time off the bike. I was perturbed and in a general malaise due to the anxiety created by being off the bike. The final thing I noticed was that no matter how tired I was, or stressed or pissed or whatever negative feeling I was experiencing - well, those went away after a few miles on the bike.