While facebook no longer lets you use ungendered pronouns, google plus does support them:

If you decide to make your gender private on Google+, we'll to use gender-neutral language to describe you whenever someone else encounters gender-related information about you but doesn't have permission to see your gender. For example, instead of saying 'Greg added you to his circles' or 'Frances added you to her circles', we'll say 'Greg added you to their circles' or 'Frances added you to their circles'. Yes, I know this is grammatically questionable. You don't need to message me about it. We value helping people control their privacy as being much more important than being grammatically perfectly. -- Frances Haugen, Google Plus Project Manager

Now that I think about it, I believe I've seen facebook using singular they with a named antecedent ("john smith changed their profile picture") more recently than 2008, but I can't find any examples looking through my newsfeed.

Update 2011-07-19: Mog says facebook doesn't know their gender and they have "Margaret changed their profile picture" on their facebook profile from early may. Not so hard to rephrase: "Margret [has|chose|picked|got] a new profile picture".