I've used flash on 2 Android devices. My experiences so far:

* On my Nexus One: Yes, flash is to slow to be worthwhile, and input tends to be awkward on the small screen anyway. Uninstalled.

* On a Xoom (running 3.1): I just downloaded flash last week to watch a couple episodes of Legend of Neil while I was at lunch. Playback was great, about what I would expect if I were using a small screen netbook or something like that. I was quite glad I had the option to use flash. My browser is set to only load plugins on "click", so I get the best of both worlds really (not sure if that was the default or not). Flash only loads when I want it to, but it's there if I do want it.