A few month ago, I came across a Java library to access the Macbook Trackpad. At first it might seems useless but when you think a bit about it, its basically a multitouch (up to ten points), pressure sensitive surface! Which opens a lot of possibility. What's more acceding the absolute coordinate of your finger is something that you can't do only with the basic mouse support of Java, because the software is made to move the move according to relative change.
Personally, I made a little scratch App which use the absolute location to (try to) give sensation close to what scratching really is. But run the example sketch and you will get how powerful this thing is!
I putted everything on my git, here.