As you probably already know, I tend to prefer to do text-based things (email, chat, BBSing, etc.) using a program which resides in a terminal window rather than something with a lot of GUI around it. There are a few reasons for this, including that they tend to have better support for a keyboard-driven interface rather than requiring the mouse for some actions. The main reason these days has to do with my having (finally) discovered screen.
Screen is a beautiful program which lets you treat one terminal window as as many as you like, and also lets you detach from the real terminal and still keep all those applications running in their, errr, pseudo-pseudo-terminals. Which means I can have my im client (if it runs in the terminal) run on my home computer, and attach to it from anywhere with an internet connection, so I never have to log out. And I get the whole thing, the real UI for the chat program, because I'm really attached to it, not just some hacked-together command-line remote control interface.
( It gets more technical from here... )