The battery life on the Pre is far from enviable.
When I set my phone up, I used the default email settings for gmail and exchange mail, told it to prompt me whenever an app wants to use the GPS. I haven't used the Wifi yet, and keep the screen at about 30% brightness with 30second timeout. I do use the Pre often for email and occasional instant messaging (I keep IM logged off when I'm not using it, I hear there's a bug that can cause the battery to drain when logged in), but I don't believe any of this is unreasonable usage.
Given the profile above, I've found that the battery is nearly dead or dead by the time I'm going to bed, and I need to charge it every night. Palm does have an extra battery charger that you can purchase as an accessory, but the back of the phone isn't designed for frequent/easy removal i don't believe. It is nice that the phone comes with the USB charger so you can charge it on your computer during the day, but I'm concered about days more concentrated on the road.
I will note, however, that this battery life doesn't appear completely out of the ordinary for smart phones of this caliber (I put the iPhone and G1 in this class). They seem to have comparable battery life, and until the energy consumption or battery technology improves, battery management is going to have to be a part of our regular lives.
I charged my phone all last night, to ensure I got it today with a full charge. I unplugged the phone around 7am and hopped on a conference call at 8 for a half hour on speaker phone. Then I did some light email thoughout the morning and turned on IM for a half hour around 1pm. The battery died at 1:30pm. I don't know if this is an anomolie, but I'm not sure if this would work for me in the real world.