This has been my experience also.I think I'm having the opposite experience. Battery usage was pretty good before update, now not so good.
Before I got my Rezound on Monday, my Droid Pro's battery life on stock 2.3.3 was terrible, as was noted for most 2.3.3 devices (see a lot of Sony's phones specifically). I didn't get good battery life while the phone was idle or under light usage until I went to CM7. My sister downloaded the new update and said it was about the same - which she said is good enough for her (she's on WIFI all of the time though at school).This has been my experience also.