In adition to mice, stylii and touch screens, I've heard requests for an API web sites could use to get detailed touchpad data (rather than assuming they're identical to a mouse).  In particular, when the hardware and OS supports it, it should be possible to receive co-ordinates for all the touch points on a trackpad.

The most interesting difference here is that the co-ordinate are not directly connected with screen co-ordinates.  I could imagine having an additional pointer type where pointerdown corresponded to putting a finger on the trackpad, and there were additional fields for trackpad co-ordinates (perhaps in some fixed range like [0,100]).

I don't think it's critical that we need to flush out the details of this scenario now, but I'd like to keep it in mind as we define potential extensibility points.