Root your phone, get Set CPU, and then run an "On Demand" power scheme.
I have my Moto Droid (original) running Froyo (2.2) at 1.1 ghz...it underclocks down to 250 mhz when it's not in use, and scales anywhere in-between depending on what I'm doing. I only charge about every other day (vs. ever day without it), or if I go nuts and play a ton of SNES or Playstation games that day, I charge it once a day. It's slick.
Also, I don't like the Moto Blur skin they have on their Android OS, I am running vanilla Froyo and like it better than HTC Sense...but it's all preference. The nice thing with Android is, no matter what device you get, you can make the OS look pretty much how you want with a little work.