[landyman]

I don't know of a library, but I have seen some sites that offer software to do it.

I'd try http://mouseflow.com/. I haven't used it yet, but it looks cool.

I used http://www.crazyegg.com/ on a project a couple of years ago and it got the job done; though it may not be what you're looking for.

[obviator]

I'm using Mouseflow for one of my sites at the moment, and I've also used CrazyEgg in the past. They're both great services, but I'm looking for some custom javascript to integrate into my own app.