Pbloore
Having a GPS in a bag, switched off but ready to be turned on when you get lost is, probably the biggest thing that scares NATS/CAA about GPS use.
If you have one, leave it in the car or turn it on before take off so its ready for you to look at, if you need a second opinion on postition.
Thief13x
Airspace upgrades are from Jeppersens database, via Garmin's website and cost about £20 a go or roughly £200 for 13. The land (road) map is in low res but you can load on hi res maps from Mapsource. These go on your data card and you need approx 64k for the whole of the UK. The detail is very high, including petrol stations and all sorts of other info. You can turn much of this off and can declutter the screen too. The manual says that it doesn't like being a road nivigator with Mapsource enabled, but it works pretty well, only getting lost if the low res road is some way away from thetrue position.
196 are about £550 and are very good. The 296 has coloured terrain maps, but I always fly VFR so don't need this function.