I own a Magellan Meridian Gold, and I installed Mapsend TOPO in the US.
For serious mapping, I purchased National Geographic Topo California Series. http://maps.nationalgeographic.com/topo/state.cfm
NatGeoTopo is very user friendly with my GPS. I can upload waypoints, and hand created routes, very easily.
My primary use for my GPS is for geocaching, and the topo programs make rugged land navigation far easier.
Here is an example of the track or "bread crumb" feature of the GPS, when combined with NatGeoTopo. This was from a hike I made to the top of Burnt Peak
http://img.groundspeak.com/cache/log/a130fbbd-ed7d-448c-83f7-dd662d8359ca.jpg
