If you are running pidgin-facebookchat make sure you keep an eye on your bandwidth usage.

There is a known bug in version 1.47-1 (which is included in Ubuntu 9.04) that causes huge amounts of network traffic to the Facebook servers. In my case "huge" means "30 GB in less than 2 weeks".

Fortunately the jaunty-backports repository contains a fix so all you need to do is to make sure you have selected "Unsupported updates (jaunty-backports)" on the tab "Updates" of "System > Administration > Software Sources".