1- Safari, internet based stuff.
2- iTunes, iPhoto, entertainment stuff.
3- Adium, Mail, iChat, chatting mail stuff.
4- School stuff: Pages, Keynote, TextEdit, Word, etc.
Spaces rules!
Space 1: Empty by default, filled up when I open Pages, PS, etc.
Space 2: Vienna RSS
Space 3: Safari or current web browser
Space 4: Mail, Skype, Twitterific, Adium
Space 5: iTunes
Space 6: iCal
I use Space 1 for work-related tasks; Space 2 for entertainment stuff; Space 3 for any overflow related to work that I may only use a couple times; and Space 4 has been used like twice in the past four months (since I got my system)