have a EVO 4G, and gotta say, I wasn't blown away by the interface. Sure I like the customizations you can do to the home screens, and the sheer amount of apps I have on the phone. However, the force closes, the constant restarting for no reason (did it to me about 5 times now, since I got it on June 8th) makes me think there's much to be worked on with this system. Keep in mind, I have not rooted the phone, but downloaded "official" apps in the market place.
I've had a Win Mobile 6.5 (800w) and a HTC Touch Diamond. The Palm 800W wasn't too bad, and the HTC Touch Diamond was a complete mess. Going from the Diamond to Palm Pre was like a breath of fresh air, where NONE of my apps crashed, and I rarely got that "too many cards" problem. The whole OS of WebOS just feels more polished than Android OS 2.1 (haven't tried out Froyo) but on initial reactions, it just feels like Android still needs some ways to go...
I will say this: I messed with a ZuneHD, and I was VERY impressed with the OS. Though the lack of a App Store (Market Place or whatever they call it) is quite a bit of a downer, the device was the smoothest/most responsive touch screen I've SEEN. Even more so than the iPhone 3G. About the same level as the 3GS. Can't help to think that the consistent 60FPS screen helps it out big time. When I got the EVO 4G, I was expecting the same "ZuneHD" smoothness, since everyone's been screaming about how awesome the the performance of the EVO 4G is. Well, when I finally got it... wasn't impressed by it at all... In fact, I was kind of disappointed, and kind of wished my Palm Pre didn't get hit by salt water! I really wanted to go back to WebOS. But alas, I'm stuck with the EVO 4G... Having the light leak didn't help it's case too! I didn't mind the light leak, but having dust get in the device is pretty bad...