Yes indeed — for whatever reason, Facebook.com is down.
There are a couple of places to verify this, independent of Sonic.net:
(Please note that these sites, too, will be sporatic, as everybody checks to see if Facebook is, indeed, down.)
These things happen sometimes, and I’m sure they appreciate your patience as they scramble like crazed bunnies to fix things. 🙂
Update: Facebook.com is back up.