It's cool but you're better off with an actual GPS built for the task.
If you like to go hiking you'd be better off taking a more rugged hiking unit.
If you'd use it while driving then the non-touchscreen PSP controls will get in the way and it's not a good idea be screwing with that while you should be concentrating on the road.
It's kind of like having a Garmin GPS that can play games. Yeah, ok, there's a computer there with a screen and an interface and it could (and does) play some games but really, I'd rather have a device built for playing games like the PSP.
Still cool, though - You'll get no argument from me on that one.