I completely second Matthews suggestion regarding xda-developers.com. It is the absolute best site to make the most these phones have to offer. These phones are absolute powerhouses and it is a pity not to take advantage of it.
Come to think of it, the thunderbolt almost resembles my T-Mobile HD2 (except for the camera specs) and it is a phenomenal experience while running Android 2.3.3 with Sense UI. The odd thing I like about my phone is that I am just a couple of minutes reboot away from running Windows Mobile, Windows Phone or Android. But of all three OS's the Android OS is in my experience, the most polished and competent.
Anyway, may I suggest you look into Navigon GPS software for this unit? Don't bother with the other entries (like Co-Pilot Live 8 or 9).