My wife and I are still in kind of a wait and see mode. I'm reading about a lot of serious issues (calls failing, bad battery life, lagging more than 1.5) here and on the Sprint forum. My main reason for upgrading would be for voice to text but I don't want it at the expense of good functionality with other things (especially basic phone functions). 1.5 is running pretty good for us.
There seems to be such a widely varied experience between users that have done the upgrade, from "I absolutely love it" to "I hate it and want my old phone back" and everything in between. If I could turn back after trying 2.1, I would do it in a heartbeat but once you upgrade you're stuck with it, like it or not. I've been looking forward to this release for a looong time like everybody else. It's killing me not to just DO IT!
I may volunteer to be the "guinea pig" for my wife and some friends with the Hero and take the plunge soon

More reviews by the brave souls that have done the upgrade would be greatly appreciated!