I'm with twistedengineer
I've tried the GPSIII and found the map a pain.
I have a cheapo Magellan GPS315. 500 waypoints, comes with a database of towns so you get the equivalent of a moving map but with towns and airfields (and any user wayponts you care to put in) marked on it. Very easy to relate to the chart and see where you are.
It has a rubber sucker mount and will run all day on a pair of AA's. Also have a serial cable to plug into my PC and Datasend on CD to upload worldwide waypoints from. There's also a shareware package called Magway which allows you to build your own databases and upload/download.
If I wanted to I could plug the serial port into a PC of some sort and get a full moving map display. Tried this with Microsoft Autoroute 2000 on my laptop and it told me I was driving up Portsmouth Harbour when I was on the M275. Not the fault of the GPS position, the digitised map in Autoroute is inaccurate.
There have been a lot of complaints about the accuracy of the airspace info in GPS databases. High resolution maps require a lot of memory so what you tend to get is things that approximate to the real thing but are not precise.
New CAA charts come out every 6 months, how often do users update their GPS databases and what Quality Assurance is there to ensure that the databases match the UK AIP?
It's an area that the CAA are taking an interest in at the moment.
Mike