I've never tested my phones battery power under constant GPS use from full charge, but I only switched on the GPS once I was 1 hour away from my destination, and I saw a 20% drop in my battery during my 1 hour use, whch I could say would've given me a 5 hour use had I used my GPS constantly. It would obviously improve if I'd switched on flight mode, but dint do that. Shawndh your not going to be dissapointed with the HTC. And when you recieve it, you'll admire it's size and compactness, because its only 108mm long. The build is obviously top notch and its TI processor is easily overclockable to 240mhz should you feel the need to run multiple apps at once, this drains the battery a bit faster, but you shouldnt be doing this all the time, chances are you wouldnt find the need to do so.
Also, I've successfully installed and run skype off my P3300 and it worked flawlessly. Took a tad longer then I expected to 'load' up, but after that, crystal clear conversation. Dont knw if you'd ever use it for that, but another use.
All in all, the GPS works amazingly well (Sirf Star III chip is very sensitive). and Since your getting the NA maps as well, you should have no problems using it at all. I live up in Canada and I used this to get from Toronto to Montreal (2 metro cities here). I was quite impressed with the preciseness of TomTom6 + Sirf Star III.
Feel free to ask any more questions.
PS: I've had the fone for a little under 2 months only so far. I'm also exploring all possibilities with my phone.