In general I already assumed that all my data was being captured, either by my country's spying or USA. PRISM is hardly surprising, in terms of the data that is (probably) collected.
What I may consider is switching from Dropbox to some other solution, as I prefer my actual files to be more private. Email has never been secure so no change there really (using Google Apps at the moment).
On actual social networks I am reasonably careful with what I share already, not so much concerned about NSA & friends but rather sharing stupid things may get you in trouble with future employers etc. Things that could get you fired are better left off public/Semi-public networks (complaining about bosses etc).
On a side note: I am happy the potentially dangerous individuals are using FB etc. It enables effective monitoring of such individuals. One example is Swedish citizens going to fight in Syria, for the rebels and for Islam (jihad). Some of these have a Facebook group where they post photos, status updates and friends of theirs(?)/supporters comment. That is pretty much free surveillance, and a good thing.
