I've loaded up Ubuntu on my original Transformer.
Granted, it has a Tegra 2 CPU, which to put it mildly is not very powerful, but Nvidia has put out the required source and modules to put up a Linux distro which takes advantage of it.
Maybe Ubuntu just has gotten "bloated" over the years and everyone has failed to notice because all PCs are overpowered these days, but when I booted it up on the Transformer, a machine which runs Android flawlessly, smoothly and responsive, I was severely disappointed.
Everything. Was. Dead. Dead. Slow. Prepare to wait multiple, multiple seconds to open that terminal. And please don't talk aobut browser-performance. Ouch.
Maybe it will run better on the newer models, but trying it out in real life was a little off-putting. On the other side: If Canonical is putting in effort to get it running well on the Nexus 7, it should translate to an overall performance-improvement across the line.
And that would be welcomed very much.