This is a great map tool! I love the variety of layers! The visitor maps are helpful for finding big obvious things like the Kaspian campground in Tahoe outside Tahoe City and other non-topo related items.
The historic maps are also really fun and the satellite with contour lines and elevations are awesome too!
The USGS topo vs. USFS topo maps are interesting as well. I didn't know that the USFS maintained or made their own topos. Very awesome!