I have just taken my 770 back from 2007HE as it just randomly reset itself all the time, if it didn't manage to run out of battery power first. Maybe I was unlucky, but it was the second time I tried.
Still, I picked up a 810 on ebay tonight

Maemo mapper works pretty well on the 770 though (assuming you have a memory card - they are pretty cheap), I went around the states with it (with googles maps), although I didn't use a gps thing (but I could have done).

I don't know how many devices can bluetooth at the same time, although it would be bad if it was restricted. I have only tried the keyboard, the phone and a ODBII connector