This is very disturbing. For once, it means that the Iranian authorities are paying very close attention to what's going on Facebook and Twitter (which, in my opinion, also explains why they decided not to take those web-sites down entirely - they are useful tools of intelligence gathering).
Second, it means, as far as authorities are concerned, our online and offline identities are closely tied and we have to be fully prepared to be quizzed about any online trace that we have left (I can easily see us being asked our Facebook and Twitter handles in immigration forms; one of the forms I regularly fill flying back to the US has recently added a field for email address).
Third, this reveals that some of the spontaneous online activism we witnessed in the last few weeks - with Americans re-tweeting the posts published by those in Tehran - may eventually have very dire consequences, as Iranians would need to explain how exactly they are connected to foreigners that follow them on Twitter (believe me, I've observed enough bureaucratic stupidity in Eastern Europe to know that even some of the officials who follow Twitter activity on a daily basis may not know how it works).
I am curious if there have been other reports of foreigners being asked about their social media activity on traveling to authoritarian states. Any ideas?