I was on Facebook back when you needed an .edu email to sign-up. I stopped using Facebook earlier than most as well - I saw the privacy issues coming.
Facebook would periodically add "new" features that were nothing more than a split of an existing single feature. In doing so, privacy settings were reset to the lowest privacy. I grew weary of having to reset my privacy settings so often.
At that point I started to leave. I still have my account, but rarely use it. I removed all my photos, and deleted most posts (and found deleting them only hides them - you have to go a step further to actually "delete," and that isn't a true delete either).