OK! I have an update that may be useful....
Galaxy S2 was running stock but rooted for a couple weeks, then changed to UnNamed about the same time I got my spare batteries and chargers in from China. Starting then, I was getting lousy battery life.
Two days ago, I decided to try out CM7. (I am so unhappy my camera doesn't work now tho) Battery life improved a noticable amount, but was still not good. I found a post, maybe earlier in this one, that talked about resetting your battery meters and being careful about reflashing because your new ROM starts out thinking that the battery is at 100% when it first fires up. I reset my battery meter and between that, and flashing to CM7, I went from putting in a fresh battery at 10pm and awaking at 5am to a dead phone, to getting about 30+ hours out of it.
So I have deduced that:
1. Flash matters. I noticed a huge difference on my EVO a whle back as well. As much as a 100% to 200% improvement.
2. That battery stats thing matters. Play around with it. Figure out how it works cuz appearently it makes a HUGE difference.