AnyGeo and OgleEarth both post today on TakItWithMe, a new free web service that lets you upload Google Maps MyMaps KML data directly from your browser to a GPS unit. It’s limited now to Garmin units, since it relies on the Garmin Communicator plugin. And while the device support page indicates that some serial interface GPS receivers will work, Garmin says that it works best with USB devices, and doesn’t promise good serial support.
For other GPS manufacturers, and for KML files created in Google Earth or by some other means on your local computer, I’ve posted before about a number of free ways to upload KML file data into a GPS unit:
Exporting Data From Google Earth To A GPS Unit
Using GPS Utility To Import/Export GPS Data To/From Google Earth
GPS Trackmaker: A Better Solution For GPS Export/Import With Google Earth
There’s another way for Garmin units, but I’m waiting until it’s out of beta to post on it ….
Addendum: Google Earth Blog points out that TakItWithMe can also convert KML files to GPX format, so that you can upload them to a non-Garmin GPS using any program that accepts GPX, like EasyGPS or GPS Trackmaker.