Want to second what Mark said here - I despise X - it's obsolete, slow, a big hack. It was useful in its time, but it's useless for now. Ubuntu eventually must run atop Wayland on the Nexus 7, or it will be a joke. I'd go as far as saying that right now Ubuntu w/X on the Nexus 7 is a far bigger joke than Android. Android at least redid the display server and removed the dependency on X, much as Wayland is trying to right now, except Wayland can really crack the dev doors open - and it won't be just Java/Dalvik but any language will be used for Nexus 7 or any other tablet. That's the future.
I'm kinda with uid313, I bought a Nexus 7 (partly due to good word of mouth from people here on Phoronix) and I think it's great. However I see it as a pure 'consumer' device and as such I use it for watching video, reading books, playing some games etc. I just can't see anything that Ubuntu on my Nexus 7 would offer that would make a difference in what I currently get based upon my usage patterns with it.
Then again it's tinkering, and it's always fun to tinker
Either way it's interesting seeing Canonical being so gung-ho about getting Ubuntu onto the Nexus 7. And of course it's brilliant that installing an alternative OS on this device is a viable option.