I have the e310. It's a great machine and the
only PocketPC that I feel is worth buying. See
this post for my feelings about PDA size and you'll understand why I say that. The e310 is the first PocketPC to reach Palm V form factor and has decent battery life.
But, AFAIK, there is no GPS that will work with it. I had a Navman sleeve for my iPaq that I liked. It's possible that there will never be a GPS that works with the e310 because I'm not sure it's sync port can be used as a generic serial port. There was some debate on this at
BrightHand but I don't remember the conclusion.
-Dylan