This thought occurred to me. Wouldn't it be nice if I could just open google earth, define a rectangle covering a place of interest, and then saving it as a map that I could transfer to a gps. With all the stuff you can do with GE I'm surprised they have not done something like this. I've dabbled with creating my our maps but I never have much luck with them and they never turn out as nice as the ones I've download here.
Actually Garmin's new "custom map" format for the Oregon/Dakota/Colorado/62/78 series is pretty much what you describe. There are some special tools to use for this now, but originally it was conceived to work with Google Earth. See this: http://www.garmin.com/garmin/cms/site/us/onthetrail/custommaps#fragment-2