These new smartphones don't get anywhere close to the battery life of old non-smart phones. I could get up to a week on my old feature phone, but a day to maybe two (when we get 2.2) is about what you can expect if you tweak a few things. Get used to plugging in your phone every night, all the power these phones have comes at a price. Plus I'm sure you're playing with your phone a lot right now since you just got it :P.
If you're getting bad battery life when the screen is off go into Settings>About Phone>Battery Use>Cell Standby and see what the "Time without signal says". If it's 50% or more then you have the bug, it's a common Android bug for phones without Froyo. Just toggle airplane mode on for a few seconds after you reboot your phone and it should go away.
The GPS is kind of fussy at the moment, the Epic has a problem with clearing old data out of the cache and so it has a hard time picking up satellites. There's a few workarounds to this like going into the GPS menu and changing how it starts up (personally it didn't work for me), rebooting the phone always works, but if you use the GPS a lot then it works fine. For me it worked about 70% of the time until I rooted and installed a program to clear the phone's cache every few hours, now it works 100%.
Don't be intimidated by rooting either, it's really easy now with all the good One Click setups. I did it on my Mac and it took no more then 10 minutes, unrooting is just as easy. I honestly wouldn't worry about voiding the warranty, until you get into flashing roms/kernals you won't be messing anything up if you want to root to get rid of bloatware etc.
Sprint's other phones like the Evo are nice too, but the Evo has it's own set of problems. Personally I love my SAMOLED screen
and we should
be getting Froyo soon.