Trillian Wikipedia Integration
I'm chatting with my buddy Micah who will ask me a question and then annoyingly answer it himself immediately after. For example, he asked me how FireFox picks up an icon from web pages. I replied that there's a favicon protocol but that I didn't know the details. He then proceeded to explain how to format the link tag properly.
Apparently the latest version of Trillian will highlight words with links to their definition in Wikipedia. So as you chat with your friends, you become a living breathing dictionary. That's a rather nice feature for IM conversations.