My 3gs is 10 days old and I'm experiencing the somewhat fast battery discharge too. I had no applications installed, no mail, push, location s., 3g, wifi, notifications all off. The battery was completely drained and recharged two times.
For example, fully charged put on standby overnight -> morning: 97%.
Wrote one sms in the morning-> 96%.
Used safari over edge (as wifi and 3g is turned off) for 15 minutes-> 91%
One call and three texts later ->89% (icon lost a pixel row too)
Barely managed to get it home with some charge left.
Two days ago I fully charged it and immediately wrote two texts -> 98%
But that would probably somewhat acceptable to a user who had his first iphone. But I have iphone 2G for almost 2 years now, and I did completely the same test and the difference is staggering. The battery indicator stayed full for at least twice the load. And one of the reasons for getting a 3gs was that the battery life on my old iphone was considerably shortened with time.
Of course I did try all the suggestions (reset all settings+redownload firmware+restore as new etc) but nothing of that worked. I seriously doubt that the problem mentioned in the tread is really connected with "corrupted backup". The problem may be software related but as far as I'm concerned it makes no difference to me. I'll probably return it next week if nothing goes any better. I'm not even sure if I'll wait for the "repair" because those take a month here.
Here is how the drainage issue was solved after my experience upgrading my iPhone 3G to 3.0.1, and three days of surfing on the web for a single coherent solution, and I didn't want to go over and reset factory values or lose functionality, no push, no mail, no Blue, no iPhone. So this is what I found in my case a single App (Frings) I started to notice that after the upgrade this application without being active was notifying me of incoming messages from my friends, at the beginning I thought it was cool and maybe a plus on the new 3.0.1 release. So I decided to remove Frings from my iPhone, restarted and test for two days if the battery behaved normal and for the sake of God it did, back to normal use. My theory is that some logic on installation process is allowing pieces of other Apps code to reside on OS layers not supposed to be, then once you remove them and install them back the issue is resolved. Hope this helps to others as I mentioned before, there's no coherent and single solution for this battery issue on the web.