This thread appears to be relevant: http://forum.kde.org/viewtopic.php?f=230&t=112102

1. Facebook has acknowledged the problem (if indeed it is the same problem, who knows) and will fix it "in a couple of weeks"

2. There is beta.chat.facebook.com one could try (but apparently it sends replies as "chat.facebook.com" which confuses telepathy).

3. There is a patch for telepathy-gabble which ignored the "didn't receive a response to our disco request: disconnect" message. If I apply this to the Debian squeeze package, empathy will connect (on either beta.chat.facebook.com or chat.facebook.com) but I do not see any contacts (there are some online contacts in the web chat). The debug protocols imply a successfull login, though.