In my own experience, it seems to be a good idea to fully drain, then fully charge the battery on first cycle. After that, you can do pretty much whatever you want, with perhaps the occasional "recalibration" as Apple suggests (they suggest it monthly, I suggest it yearly).
I have an almost three-year-old Blackbook that stays on the mains 90% of the time. I almost NEVER run the battery down to zero, indeed its rarely on battery at all. It's still giving me more than three hours of real-world "normal" use on battery.
Maybe I'm just lucky, but my 2.5 year old iPhone behaves the same way, as does my wife's five year old iBook G4. Coincidence? I don't think so.