My account was recently flagged for basically adding too many people to my friends list in a short period of time. My activity was described by facebook as "suspicious and annoying." as their explanation for why it was flagged. Here's the kicker, Facebook kept shooting out friend suggestions in a projectile manner one right after another. So I simply added the people they suggested as I was thinking "Hey I know this person." and many suggestions were the same people who were already on my list or people I had already requested. My advise is simply be careful and don't engage in too many or the same activities at a time.