I have the Sprint Hero and a pretty happy with it. It certainly is underpowered for what is running on it (supposedly the android 2.1 update will improve performance though); it's usable, just not the snappiest thing in the world (I assume disabling HTC's Sense UI should help, but I'm happy enough as-is). The guys over at XDA are pretty far along with Android 2.1, so if Sprint doesn't provide the update soon it might be ready (or close enough for me) from them. Also, there is a rumor of a Sprint/LG/Android phone to be announced at CES.
I'm having envy over the Nexus One though. I'll likely opt for an upgrade once Sprint gets a Nexus One (or like) device and sell the Hero.
Oh yeah, in terms of functionality It's basically that same. Biggest thing missing that I really would like is Google Maps Navigation -- Sprint Navigation is doing the job for now though.