My co-worker, who works in the building across the street, uses AIM for communications. Since we're running Linux, I tried to get Pidgin on my box. Unfortunately, the work box is Ubuntu Dapper Drake, and it only has GAIM. (At least it's better than the Red Hat Enterprise Linux 4 box I had to start with.) Weirdly enough, it wouldn't connect to my Google Talk account, although my Debian Unstable box at home has no problem with Pidgin (GAIM's sucessor).
I tried multiple solutions. I fooled around with every setting. Being the Alpha Geek, I tried downloading the Ubuntu source packages, but the support tools aren't available in Dapper. I tried comparing the configuration with my home box, thanks to SSH. I even tried logging in manually.
What finally fixed the problem? Google Talk can use port 80. Yup, work must be filtering port 5222, and I couldn't even tell from my telnet sessions. Some alpha geek I am.
The kicker, of course, is that I can't connect to his AIM user from my Google Talk account. I had to register an AIM user to connect to him, rendering the whole thing moot. Well, mostly moot: I can now IM with my wife, anyway.