I'd agree with every other day. Back before I found road biking for relieving stress, I was a pushup junkie doing 3 sets of 90 six days a week. I probably woud have been better off doing less pushups, slower and concentrating on form which is what I currently do (3 sets of 30 about every other day). Keep your head up (enough so that you can touch your chest to the floor without your chin/nose hitting first) and go in slow, controlled motions. Pushups are way harder this way (as opposed to head down, and going as fast as you can) but you'll get just as strong with less stress on your wrists and without fear of smacking your face on the floor (yes, I've done that a few times, alcohol and pushups don't mix).

I also found that the best way to increase your reps was to get in your head how many you are going to do before starting a set. Even if you have to stop and rest in order to finish, make sure you complete the set. The next time you try for the same number, you may only get one or two more before you need to rest, but eventually you get to the desired number without stopping. Then increase it again. It's fun, I swear.