I've got a Garmin 60C, and works just fine! I have a copy of Mapsource with North America loaded in it, and that will transfer to/from the GPSr just fine.
However, I got a copy of the European maps from a friend of mine and I can see all the wonderful maps on the computer, but I cant transfer them to my GPSr. It says "Some devices were found, but they dont have the capabilites".. which I think is just garbage. It works just fine with the North America maps, just not the European ones.
P.S. Mapsource does see my GPSr in the "Get Unit ID" menu thing...