I purchased this phone after losing my Treo 650 in the Grand Canyon. And yes, I used the correct preposition in that sentence. Having been a Treo owner previously, my learning curve for the Palm platform was minimal.
I immediately noticed better reception and sound quality than the 650 was able to deliver. And all without that annoying nub antenna! I don't use a lot of the extra features, but am a heavy use of the email program (no change over the old one) and built-in IM. It works great for that, now that you don't have to log in to send/receive messages.
I do have two complaints, and they are minor:
1) The phone didn't come with a mini-SD card. I still need to get one. But since I don't put a lot of apps on the phone, it's not a huge deal.
2) On occasion, I won't be able to hear calls. When I make a call, I don't hear it ring on the other end, and I can't hear the person when they answer. I just remove the battery to restart the phone and it works fine. Only happened a few times, so it's hard to recreate.
Other than that, I'm very happy with this new model. Agout the size of my iPod, but a little fatter. Easy fit!