Huge screens and widgets are a recipe for killing batteries. Definitely some apps and carefully going through the settings can help a lot.
I was looking at some message boards about it and it seems that reports on battery life are all over the place. One big factor seems to be using the phone to actually make calls. A real battery killer right there.
The vibrant is rated better for battery life than my phone. When I first go mine, I was out of juice every night. After some adjustment of settings, I have about 50% left every night.
My wife had not modified anything and she got all day use from one charge from day one.
One downside to the vibrant is that is does not use micro USB for recharging, it uses one of the Samsung plugs. You will probably read micro USB in promotional material but it is not. Mine is micro USB which I think is much more convenient, I had about 5 unused micro USB cords before I bought my phone.