I'm having the same problem with battery life. I'm trying to recall what I did 'cause I did mess it up a bit when I upgraded. I was waiting for JB but it didn't come out the first day, so I went ahead and upgraded 3.0 (my phone is 8gb 3G officially unlocked.) went to bed, didn't notice anything wrong. The next day Pwnage came out, so I JB'd it. I recall when it was restoring that the phone got kinda unusually warm, but I attributed that to having lots of files to restore (you know, like copying lots of files on your HDD's)
Now, I had google sync push for contacts and cal running before now, and it was no problem (cept for the data bills) but now (yesterday) it was like 50% from full charge after 3 hours. So now I'm searching for peop having the same probs, and it seems there are. The thing is the reports are so very different from person to person that I can't seem to get to the bottom of it. I'm going with push turned off today and will see what happens, but there's a discussion going at apple board:
Apple - Support - Discussions - Original iPhone 3.0 upgrade - No ...
I haven't read all of the posts, but thought someone might find it useful.
BTW, some people seem to think it's to do with Spotlight indexing stuff, and I have to say that kinda makes sense too. We'll see
Ta!