I've had the Sprint Palm Pre for ~13 months now. It had some initial problems with build quality of the first batch, but after the warranty replacement I have had no problems for the past year. Early during June I upgraded to the HTC Evo 4G. The Evo is a very sweet phone in many respects. It is very clearly one of the best phones on the market now along with Droid Incredible, Droid X or Samsung Galaxy S. But I had three key problems:
The Evo is too huge. With the 4.3in screen it crosses the line of acceptable upper bound size for a phone.
On-Screen keyboard. It is simply clumsy and slow to use compared to a real physical keyboard.
The Android UI is less streamlined in design compared to WebOS. Various tasks on my Palm Pre that would take mere seconds would take 5X as long on the Evo. I found myself missing the sweeping gestures of the WebOS interface. I do not need to press upon precise locations on the screen to go "Back". Multitasking between apps on WebOS is very smooth with the card sweeping gestures.
Having used the HTC Evo 4G for a month, it became clear to me that Palm put a serious amount of good design into the usability of WebOS. There is a lot to like about the WebOS platform. Hackers have seen how friendly Palm has been toward developers. FOSS developers have commented about how Palm used various Open Source components like upstart and pulseaudio a well integrated fashion. If WebOS had launched a year earlier and with fewer initial hardware glitches, it might now be a serious contender to Android. But various indicators now show that Palm simply lacks the momentum of customers against the likes of RIM, Apple or Android. Palm is heavily investing in their app ecosystem, without which they have no chance. It remains to be seen if HP's continued investment will keep the platform alive.
I returned the HTC Evo 4G under Sprint's excellent no questions asked 30 day trial policy. The Evo is a very good phone, but I'm simply more productive with the streamlined interface of WebOS. I think the ideal phone would be a larger Pre, with horizontal instead of vertical slide-out keyboard and modern 1GHz processor. Unfortunately it seems no such device is in the plans. HP seems to be working on a WebOS tablet. I might consider the Samsung Epic 4G. The slide-out horizontal keyboard might make it usable enough for me to tolerate the UI negatives of Android.