Don't forget though that most Palms or Pocket PC devices were designed to live in a 'pencil pusher's' shirt pocket, and not be knocked around as much as an aviation GPS unit.
I take it that you want something portable for a light single or twin.
I used a Garmin 92 for years that was really knocked about in Top End charter use, despite my efforts to look after it. I would be surprised if my Palm could take as many knocks as the Garmin did. Eg leaving the thing inside a locked up aeroplane in 40 deg heat for an hour or two would just about melt the screen, and accidentally poking it with the ceremonial spears you are trying to load in the cabin, etc, etc.
That all said, the combination of a fully programmable device with GPS input would have to be a powerful combination provided you put the time in to understanding how to use it.
Just my 2c worth