[UPDATE: As you may have read, Facebook was having its own problems today which were separate from Twitter's. As some of my Facebook friends seemed to be using Facebook just fine, and I couldn't, I wondered if it was because, for many of us, the two platforms have a bridge between them. I was wrong. BTW, one friend pointed me to this story, which notes, among other things, that right now there's a big hacker convention going on. Just sayin'.]
Right now we're in the equivalent of a major power outage, if you're into social networking that is. Not only is Twitter so down that its infamous "Fail Whale" seems to also be down, but, from what I can tell from my own experience and that of a few others, people who have their Facebook status updates and their Twitter accounts linked are experiencing major problems too, presumably no matter where you are on the globe -- a friend just reported the same problem, from Greece. Twitter, on its status blog, is calling this a "denial of service attack" and says the site is up (not in my experience, at 11:25 a.m. EST), but that it is still recovering.
As for the Facebook problems, here's how extensive they are: not only am I finding it impossible to post status updates, but there are also problems with commenting to someone else's status update, and even sending email to someone else within Facebook. One of my Facebook friends was able to post on my wall, as a last resort; it doesn't appear that I can do the same. What's strange, and troubling, about the Facebook problems are that since it's only supposed to be status updates and tweets that are linked, it would stand to reason that the Twitter problem would be limited to that function, but it's not.
More on this as it evolves.