Yep, I saw this interestingly articulated here: http://stumblingandmumbling.typepad.com/stumbling_and_mumbli...

In essence, the power of Facebook to connect you with your personal friends also makes you re-make how you present yourself to the outside world.

You create a "purified identity", maybe as you see it a better, less controversial character for fear of offending, or perhaps more likely to please your 'friends'.