Looks like Twitter's down as of 11 a.m. this morning: Twitter just posted on its status blog that its currently "defending itself against a denial of service attack".
UPDATE: Twitter says the site is back up, but that they're continuing to "defend and recover" from the attack. It took about an hour, but I was able to log into Twitter around noon. The problem also seems to be more widespread: Six Apart, which owns Typepad, how we run this blog, is having some problems - it seems commenting on the blog isn't working. And blog ReadWriteWeb is also reporting that LiveJournal is also down. Bridget thinks there are powers conspiring for us to actually do work today!
And here's what error message I keep getting when I try to update my status on Facebook:
Some people are getting through: Bridget reports she's able to get some messages. I'm wondering if Facebook is also being targeted or if it's simply overloaded because of more users on Facebook since Twitter's out.