I find that if I get really into something really fast and spend loads of time doing it, I get sick of it fast. I've found that if I purposefully ramp into something slowly, and take breaks from it before I've had enough, then I don't get bored of it. I find this is particularly true with music; I have a rule that I never listen to the same song more than once a day, unless I'm showing it to someone else. There are a few songs I can't listen to because of over playing, but almost none since I was 17 when I established that rule.

EDIT reading that back it doesn't seem as relevant as I thought it would...