I've been using iChat's Jabber support to chat with MSN and ICQ contacts via Jabber transports on an open server. Unfortunately these transports sometimes go offline, and iChat doesn't try to reconnect to them unless you disconnect and reconnect to the Jabber server. This can be a bit annoying, especially to the people who have you on their contact list and have to watch you go online and offline repeatedly.
However, I noticed that if you open another Jabber client (which you probably have already in order to sign up to the transports -- I use the excellent Psi) with more comprehensive transport support, you can sign up to the transports in the other client while keeping iChat open. The minute you sign up to the transport in the other client, the same will happpen in iChat.
So if your server tends to force you to disconnect and reconnect all the time in order to sign on to troublesome transports, don't sit there alternately selecting Offline/Available from iChat's drop-down. Just fire up your alternative Jabber client at the same time and get everything fixed.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2005051707122631