A downside of Facebook

As much fun as facebook is. I guess it has a very important downside. Lately I have some friends busy untagging themselves from pictures to prevent others from seeing some crap they got into etc.
I don't think I did anything crappy things that I am afraid of any1 knowing since for some reason I am like an open book, and tell every1 everything. If you know me for some minutes you might end up knowing my life story. However I still choose who to tell and facebook takes this away from me :(
Thinking of unregistering form facebook if possible.