I use it as a nice big pretty moving map in combination with my Garmin Pilot III which holds the actual route and shows relevant airspace.
Generally good software and shows a lot of promise. It is great for some additional situational awareness, lots of towns and villages on the map which is handy, and I like the planning features, but I will not be using it for primary nav or even primary GPS yet.
I have experienced the occasional crash but my main gripe is the poor quality of the airspace information - ATZs are not shown at all, several low altitude airways are missing altogether and could easily be run into if unprepared. It would also be nice if it could display NOTAMs.
You do need a decent sized card but a 512MB card costs about £15 nowadays so that shouldn't really be a big factor.