Two problems 12.04 solved:
1. On 11.10 I was getting frequent kernel panics when watching flash in a browser (Youtube in Chrome, Chromium, Firefox), and when watching video in Movie Player. That's all gone.
2. In 11.10, Ubuntu Software Center was sluggish as hell, so much so that I never used it. It's much faster now, just a smidge away from being downright snappy, and hence useable finally.
I like how the upgrade (via sudo do-release-upgrade -d) resulted in what seems to be a really clean installation, and that I didn't have to do a fresh install to get that (still scarred from my Windows days).
I hear battery life is improved as well but haven't tested that yet. Hope that's true.
This is on an hp dm1-4050us, Intel i3-2367, HD3000, 8GB RAM, 5400rpm hdd.