I don't worry much about drivetrain wear; I lube and wipe it on a regular basis, but other than that I ride it until the chain starts to skip and then replace it together with the casette. The shifting, of course, gets worse towards the end, but as I live ina flat place, that doesn't matter much, and the need for little overshifting when downshifting a few times during a commute isn't too terrible.
Other parts I like to have in order though.