I had the incredible for 2 weeks, DX since thursday. The only reason i traded in was battery life, because it would be cheaper than buying a new battery.
Incredible:
I shut down any apps that i previously downloaded and some of the preloaded apps, leaving only grooveshark running for an entire work day (8-4:30, grooveshark off maybe 30 min to an hour). This would leave me with between 4%-10% battery (According to battery widget).
Droid X:
I still have grooveshark running, however, i also leave other apps in the background (gmail, facebook, browser, maps, etc..) and have yet to get below 30% at the end of the work day. On its first full charge, it went an entire day of work streaming grooveshark, after work going to the bar and using it sparingly and lasted untill approximately 1 AM, and had 5% when i shut it off.
Personally, the DX was the way to go for me, i have 0 complaints so far, and the person who did the exchange at the verizon store told me he wouldnt have even sold me the incredible because of its battery life. I Hope this helps and welcome if you switch over.
Forgot to add that i use the smart phone setting.