I'm considering getting a Nexus 7 to do some multi-touch development on Ubuntu in the run-up to 13.04 (i.e., now :-).

What APIs, /dev files, or protocols are available, or could be made available with not too much work on my part? What data is available from the device?

The data I want to get my hands on is -- if I can -- the same as I get from /dev/uinput/event* from an Apple Magic Trackpad, viz:

1. positions of all touches (could be as many as 10 simultaneous touches, but much more typically 6 or fewer)
2. their size/pressure (in both x and y directions)
3. their angle
4. their identity -- i.e. an integer that is somewhat reliably preserved across touch events, for as long as a finger doesn't lift off the surface

Not all of this data is essential -- but the more of it there is, the merrier.