I use an iPAQ PocketPC with a Rikaline bluetooth GPS and cannot rate it highly enough. The memory map software is very good and has never been any trouble although I still keep a navlog for all flights (just in case).
It makes answering passengers questions on "what's that place called?" much easier, just press a button to change map scale to Ordnance Survey and hey presto. Changing your route mid-flight isn't too tricky but could be made easier. Saying that, it isn't rocket science and doesn't require any more head-down time than if you were re-plotting on your half mill chart.
I also use the iPAQ for the flightcalc software which makes the flight planning much easier and saves wear and tear on the whizz wheel which sits redundant in the flight case.
Battery life is excellent and I haven't had any trouble with not being able to view the screen on sunny days even when wearing sunglasses.
The road software TomTom is also excellent and you can usually get this bundled in with your GPS if you're lucky.
lhd