I was able to squeeze 1 day and 16 hours of out of the phone. Mostly in WiFi mode, some 4G, extremely light web browsing, lots of app installs and configuring. Lots of texting. Camera and gallery use. Power saving mode was enabled as well.
One thing that helps is that I put my phone into airplane mode at 11pm, and it comes out of airplane mode at 6am. I don't expect calls during those times.
I also noticed my battery lasted a bit longer WITHOUT using Advanced Task Killer.
I could get my old 1gen Moto droid to go about 2.5 days. Considering this phone is a lot more powerfull, I'm fairly happy with the longevity of the battery life.