They call that a Mouse Over. Most common use is for links. It is a nice little feature that helps determine if its a link or not, plus it looks cool to.
I did notice that it does work just about everywhere I go on the site.
Pretty soon the buttons will probably do the same..
Hehe, I was wondering how long it would take you guys to notice that. I do plan on adding that to thread and PM cells, but I'd like to modify the javascript so that it also "activates" the CSS' A:hover color to the text (so the text would also turn black when you put your cursor over the cell) before I implement it there. Now, if I only knew how to do it...anyone have some ideas?