Sorry forgot the most important take a look at URL.fetchAsync(function) instead of URL.fetch([location]) it would stop the widget from freezing up when updating.
I second invision power boards also the add button could be hid until mouse enter and an option to control the transparency of the background image would be nice.
vBulletin happens to be used where I hang out most. It is certainly possible to extend this widget for use with other forums, but I'll wait to see what kind of demand there is. I would also be willing to let another developer do work on this code.