I used to have over 300 'friends' on Facebook when I was in college. As you can imagine, the vast majority of those people were random classmates, former roommates/dormmates, acquaintances from student organizations, friends of friends, and random people I met at social events. A couple years ago I cleaned out my list of people I didn't communicate with on a regular basis (at least weekly).
Right now I have 60 friends, most of whom I talk to regularly. However, I'm quite sure I can afford to delete some more people because I know I haven't talked to some in at least a few months.
Oddly enough, I have very few friends leftover from childhood and school years before college. I completely moved on from everyone and started anew with friendships after I graduated from high school.