I switched from a Pre that I got on release day. I had it for a couple months, and was I guess overall happy with it. I do agree with the issues the above people made (hardware was cheap, software sometimes laggy, & lack of apps). I've been really happy with my Hero, and I'm glad I made the switch. I did question the lack of a physical keyboard (this is my first soft-keyboard phone), but I'm getting along ok. I could type faster on a physical keyboard, but Sprint doesn't have any other options at this point for me. My wife has the Moment, and that thing is a brick. I've gotten used to it, and I really don't crave a physical keyboard anymore.
I too have been a long time Palm supporter. I've owned every Palm phone that Sprint has offered, but finally gave up on the Palm OS and went to Windows Mobile, but was excited with WebOS came out and went back to Palm. It lasted about 3 months and now I don't see switching away from Android OS anytime soon.