When announced April 12th, the Trimble Outdoors layer with GPS-based interactive hiking information was much ballyhooed.
The Get Outdoors blog tells it like it is (I think):
I’m gonna file this one under Google Hype! since I can tell you first hand using Google Earth for any serious outdoor planning is useless.
It doesn’t come close to a topo for route planning …
Other than a rough overview of terrain and approaches I’m still giving Google Earth a big thumbs down for usefulness…
If you want to use some kind of computer planning tool you’re better off with Topo! or another CD-Rom based product. I couldn’t even find the trails when I booted up Google Earth. If it takes more than a minute …
Get Outdoors – Google Earth Adds Hiking/Biking Trails Layers: Yawn! – Getoutdoors.com Outdoor Blog
We all know the future of hiking is 24/7 worldwide internet connectivity, real-time blogging with geo-tagged photos.
That time is not here yet.
Modern Hiker gave the new layers feature a try:
That said, it looks like it could be pretty cool, eventually. I don’t know about your home area, but right now the map’s Los Angeles hiking trail map looks pretty dang barren.
Leave a COMMENT if you have had more success with it.
larger image – Google
besthike.com 
There is a mashup of Google Maps at http://GPSVisualizer.com that I use to create personalized, interactive Google-style maps of my hikes.
In addition to the Google map/sat/hybrid format, you can also display routes and tracks on USGS Topos and Aerials (USA only). Best of all, you can take the generated code, customize it a bit, and post it to your own website. An example of one of my hikes is at: http://www.anthonians.org/hikes/johnson_ridge.html
Another program I am thoroughly happy with is USAPhotomaps, a free program that seamlessly downloads USGS topos and aerials . . . and allows route/waypoint/track plotting, interface with GPS, etc. http://jdmcox.com/