I've done all the usuall battery saving steps. Display brightness reduced to 10%, turned off wireless when not using it, make sure all non-esential apps are shut down. With heavy use (because its a new phone and I'm playing with it), my battery is still 90% at the end of the day.
Curently having a friendly battery duel with my friend at work and his new iPhone4. We're going to go all weekend without charging and see who's phone battery lasts longer.
He just got his iPhone 4 weeks ago and he said he can already see its not lasting as long as it used to when it was brand new.