I've used vanilla Froyo on the Nexus One. It's dog slow. I don't think this problem is isolated to OEM-specific Android modifications (though they certainly don't help).
Responsiveness and framerate-wise, even a simple cursory examination will tell you: WP7 and iOS run laps around poor old Android. I got to play with a Nexus S recently, and the responsiveness is greatly improved over Froyo on N1... but is still noticeably less smooth than either Apple or MS's platforms.
It's an odd day when MS's UX is more polished than somebody else's...
One area where Android's lacklustre performance really hurts usability is diving into menus. iPhone came up with the novel idea of sliding menus - a simple animation that communicates a lot of context to the user (A belongs under B triggers modal window C, all based solely on the direction of the swipe animation). On Froyo+N1 this animation is jerky enough, frequently enough, that this relationship can easily be missed, resulting in more user confusion and worse UI comprehension overall.
Google needs to realize that we are in the year 2011, not 1995. "UI design" is no longer about placing the right buttons in the right places, and animation is often now the defining line between an easily comprehensible user experience and an obtuse one. IMHO graphics/animation performance is the #1 obstacle in Android's way, and the main advantage everyone else seems to have on it (and it's a huge advantage).
When I use a 2.2 phone, my impression is one of annoyance. I don't know if my touches will be detected, and even if they are, I don't know how long I'll have to wait for the phone to respond. Heck, I enjoy using WP7 phones more than Android because of the performance, despite the fact that WP7 is significantly less featureful than Android! Navigating WP7 is a pleasure, and it never feels like the phone stands in your way. I have yet to get this feeling from Android.