Google Earth is great for uploading your GPS data (tracks, wpts, routes), but, at this point it is too cumbersome to manually input more than a few wpts into your gps. Manually inputting wpts into your GPS is a tough slog.
Here in the states, we are lucky to have National Geographic's TOPO! software: http://shop.nationalgeographic.com/jump.jsp?itemID=247&itemType=CATEGORY&KickerID=1003194&KICKER
National Geographic has the best digital maps, but, apparently they are limited to the US.
Using digital maps w/ TOPO!, you simply use your mouse to put in wpts on the digital maps. These are then easily assembled into routes. The wpts and routes can then be effortlessly downloaded onto your GPS.
There is other software for digital navigation. Fugawi software is one that has potential to use in conjunction w/ Google Earth. You can see a description of Fugawi software at http://www.landfallnavigation.com/efugq.html
In reading that Fugawi description, the key to users wanting to explore un-digitized areas, is near the bottom:
Customize and print maps
Open a supported map, or import your own scanned paper map and calibrate it. Add routes, waypoints, or tracks, or freehand draw on the map. Print a personalized paper copy at the scale of your choice.
Google Earth immediately makes that description dated. You don't have to scan it in, simply get a .jpg image from Google Earth. Fugawa software allows you to calibrate that image using 3 wpts (obtained from Google Earth). Eureka! You have generated your own digital map to use to lay out wpts and routes within the Fugawi software. These can than be downloaded onto your GPS. (Note, you cannot download the maps, but you can download the wpts and routes.)
Hopefully, others reading this can chime in with their own experience getting wpts and route info into their GPS units w/ a minimum of grief. "grief" = manually inputting wpts.