I have a Pre and am currently waiting at home for my Droid to be delivered for my switch to Verizon. I can't comment on the droid yet as I have only played with my friends but I'll detail why I left the Pre (even knowing what the CES announcements were going to be).
WebOS is a much more "fun" OS by far. From what I've played of Android (and reviews back this up) multi-tasking, gestures, and how things works are just fun and intuitive. I am definitely going to miss WebOS in that regard.
However, I finally decided to leave because the main functionality of the phone. There are just too many bugs in the system. 3 times in the last week my data stopped working until I rebooted the phone, the contact management isn't the greatest, calendar is slow and annoyingly limited in some regards, the alarm clock is notorious for having issues (i.e. not going off), Memory leaks are everywhere due to how apps and the OS are designed, phone application takes quite a long time to come up, etc...
Also, I am dubious about 3rd party support. Google maps is absolute crap on WebOS (google hosts the code itself on their servers, so even for the UI to come up there are delays). Palm changed the API for something an Pandora no longer works with the microphone button on my headset (button is used to pause/play and go to the next track usually), and their are numerious bugs in Palm's multimedia API that makes the media players have some annoying (although probably low priority) issues.
I firmly believe that in a year, WebOS has the potential to be amazing operating system, nad when my 1 year contract is up I will give the Pre another serious look, but for now I personally was not a fan. Once they straighten out their APIs, fix a lot of bugs, and get non-half assed 3rd party support WebOS will be a force to recon with. Until then, I'll have my Droid