I had darkcoding.net setup in Google Apps For Your Domain, with the
Chat service active. Disabling the Chat service (and waiting about one
hour) fixes it. Federation works perfectly after that.
It seems Google Talk checks Google Apps For Your Domain first, and
only tries the SRV record afterwards if it finds no match.
$ host -t SRV _xmpp-server._tcp.darkcoding.net
_xmpp-server._tcp.darkcoding.net has SRV record 5 0 5269
darkcoding.net.
$ host darkcoding.net
darkcoding.net has address 70.85.31.252
And 70.85.31.252 is my own box running Jabberd 1.4. This didn't make
any difference until I disabled the Chat service in GAFYD.