After a little play time in the store and a lot of reading I opted for the Mesmerize over the Desire even though a lot of the experts preferred the Desire. Faster CPU/benchmarks, bigger screen but comfy in the hand, MUCH better screen, and better battery life! The Mes just strikes me as a more modern phone...AND I got it for FREE!
One thing to remember though, the Desire is slated to get Froyo in a couple weeks, while the Mesmerize won't see it for a couple monthes!
Note: Not sure this means anything, but after the US Cellular holiday free sale, the Mesmerize is still out of stock, (last I checked), and according to their support line will be out of stock till Feb.! While USC is still trying to move their remaining Desires!!! Tech told me the Mesmerize out sold the Desire 3 to 1
Cheers