HB
Don't know about Navstar but NavBox certainly does.
IO540
The Garmin PDA/GPS runs the Palm OS AFIK.
I've been having a little play with Memory-Map on an XDA plugged into a cheap handheld GPS. (In the car not in the a/c)
Moving map is fine but I'm not at all sure I'd like to fly with it. However I think I would like to try it with NavBox. (no it's not been released yet) It's early days but all it needs is a bit of sensible software development to provide the sort of aviation facilities currently found on a good handheld GPS.
Agree your comments re web access but again that's a developmental issue. Web pages optimised for PDA viewing would not be difficult to implement.
Memory loss on power failure should not be an issue any more. The XDA uses Secure Data (SD) cards which retain their memory even when removed from the XDA.
What would be nice is a power outlet on the panel.
Mike