I finally got Mango installed tonight. I'm impressed. Of course it's what WP7 should have been when it launched, but still.
Scrolling perf in SL apps is amazing - even ones I haven't updated. And IE9 is so fast compared to my iPhone it's ridiculous. It doesn't layout all pages correctly (even compared to the IE8-based browser in NoDo).
I still think Metro blows as a UI design though.