I've become more involved in my kids' school over the past couple of years, as I don't have a baby anymore and have more time. I WAH, so I have to be careful to leave time for that and not take on too much at school. OTOH, I know people with very demanding jobs (physician, attorney, etc.) and more kids than I have (one woman has 6 kids, two still in diapers) who manage to still be highly involved in the PTA, clubs, fundraisers, etc. So the drive/desire definitely varies too -- I enjoy being involved, but I also enjoy family down time (and solo down time!) and like to create a balance instead of saying "yes" to everything.
Anyway, my current involvement is that I'm room parent for DS's 4th grade classroom, chairing one PTA event, helping coach running club, and helping in DD's kindergarten classroom once a week. That's manageable for me, and makes each kid feel special while allowing time during school hours to get some work done.
So how about you? And what have you learned from past years in terms of managing your school volunteer time?