No, there is no difference. It can track your location, and it has directions (just will not audibly tell you when to turn etc). In all honesty the audible directions are kind of annoying after a while. I am not sure if the 8100 does this, but in google maps either way it can triangulate your location within around 1200 meters based on the cellphone towers (GPS will track you down to a couple meters, much more accurate).
In my opinion, go with the 8120 (I have one). The WiFi makes browsing faster, plus you can have GPS too
. Well its not built in, but you can pick up a bluetooth GPS for cheap from
Or HERE (This one is the one I will be purchasing)
This is just one example, its small enough to fit on your keychain, and provides the SAME features as the 8110.