I used one last year when they first came out, may have been the 300C but still, and it sucked. The thing couldn't navigate for crap. It got us lost sooo many times. One instance we had it in the car, heading for our hotel, it knew the hotel as a POI, told it to Go To. Follow its directions and where do we end up? In some dudes driveway back in the woods on the other side of town. This was just one instance of it's poor navigation. Granted we were in Kentucky so take it for what its worth.
The last one I used was a Garmin SteetPilot. I used this one in Utah and it worked great! It was soo much nicer than the Lowarnce unit. It gave accurate directions everytime, didn't once steer us wrong even driving into a new development in hills above SLC.
The StreetPilot c330 can be had for $249.99 right now at Circuit City.
Take what I said with a grain of salt, that is just my impression of these two units in other states, for all I know they could work great in California, the maps may be more detailed or.... So yea, Lowrance makes the best Off-Road and Marine GPS systems, but over the road I felt it was lacking and the Garmin worked excellent over the road but their off-road units are lacking.
Also you may have trouble finding a unit with 'waypoints' like a typical 'gps' has. I know the Garmin wouldn't show lat/lon and you couldn't map trails with it. Likewise it doesn't look like the Lowrance unit does either. For that you may be better off with a 540C and load street maps into it. But at that point you loose the turn by turn that the street units have.
So yea.. that is just my impression of these things from the few I have worked with...