I'm finding it very slow compared to CM7, though this may just be a bad rom. The UI is a lot better in some apps (gmail, gallery, calendar), though I find in other places it is worse (new task switcher, still find that 2 column market is silly on a small screen, dislike large contact photos on favorites (see less at a time), don't like the swipe randomly to see url bar in browser. Love new widget previews, but wish it was accessible by long press on home screen still. Keyboard and text selection is far better (accurate).
Not sure how much I like installed apps auto adding to my home screen. Makes it a mess on initial setup.
And what the hell happened to text reflow in the browser? I can't even read HN anymore.
The killer is the slowness though. If the real thing for Nexus S is as slow as this ROM, I'm very disappointed.
Panorama is damn cool though.
The biggest difference seems to be that scrolling is now GPU accelerated everywhere, which is particularly noticeable in the browser. The browser itself also seems much faster. It's no problem to load 5/6 tabs in the background quickly and let them render while continuing to browse in the current tab stutter-free. It makes browsing on the phone much more like a laptop/desktop.
This is all on 18-month-old hardware.
They've also made sure that the rest of the OS is much more polished. I still think the widget desktop/app panel division makes the whole OS seem more complicated than necessary, but Android has come a long way. It's finally an iOS competitor on user experience.