My battery lasts all day during a normal work day. I check my email on edge while my husband drives us to work, or check on EIC. The iphone sits on my desk at work, with wifi on, but I do not use it at work except to occasionally talk or check my calendar.
I run out of battery FAST if we are taking a long car trip and I am surfing web on EDGE, or watching movies. That made my trips boring.

I will need to get reserve battery power for this summer.