-A chat block would definitely be nice so you could put it at the bottom of your forums, for example.
-ability to use emoticons and text formatting like colors/bold/etc.
Also, I've used ajax chat scripts before that eat up the servers cpu when more then 10 people would get on. I'm not sure how to avoid this, but perhaps using some sort of cache would help.
If you're going to track using an image, a 1pixel image would probably be the best idea in case thousands of xoopers start using the module on their sites.
-Mantooth
I hate Mortal Kombat