What if the mouse served as both input and output device.
It reads the x,y coordinates and it outputs, well, heat!
We could utilize this feature to do some cool stuff.
1. Browsers can emit heat to the mouse when the visited website is new or recently updated!
2. Digg can emit heat to the mouse when the current post has rich diggs.
3. Facebook can emit heat to the mouse when the current member has too many friends or wall posts.
You may add to the list.
From a technical point of view, I don't think its difficult, we just need it to be supported in Windows and Mac to catch in fire.
Feel the heat while net surfing.