I've been running this since Wednesday. It seems faster than Eclair. A couple applications have disappeared from the Menu, while at least one new one has appeared. One app got renamed. The home screen looks different, and we've gained two, for a new total of five.
I was surprised that the update didn't wipe the phone as I suspected it might. I went ahead and performed a Factory Data Reset anyway, as I wanted to reload my 3rd party applications. Funny thing is, none of the apps I have been using allow for installation to the memory card. That's a shame because I wanted to see if app performance would change running off the card versus running off the phone. I reinstalled Launcher Pro and Home Switcher, but have not yet used either, as I like the new default launcher, and five screens seem to be enough.
One new app I've installed is Angry Birds. I've been using it on my Mesmerize, and wanted to see how it would perform on this device. I haven't gotten to play it much yet, but so far, its performance has been good.
Unfortunately, because this is a Stepping 6 version of the ARM CPU, we won't have Flash 10. Also, the update didn't give us the availability for Live wallpapers.
That said, Froyo adds better support for Microsoft Exchange OTA syncing, and the phone can now be used as a portable hotspot (with a tethering plan of course).
One thing I try to do with the Acclaim is to keep it at 100MB or better of device free space. Below that and performance seems to degrade quickly. Once below 75MB, problems like freezing and auto-shutdowns begin to occur.