Here is the text of the geometry clipmap patent application titled "Terrain rendering using nested regular grids."
The researchers who have developed this idea (Losasso & Hoppe) published an article on their technique in NVidia's "GPU GEMS 2." That seems like a pretty lame thing to do, given that they applied for the patent in early 2004. I've come across a discussion thread at gamedev where the general consensus is that it is a defensive patent and they wouldn't defend it against others who would use it. While this may be the case for most games developed, the virtual globe market is red hot and I would assume that they would use this against Google, ESRI and any other virtual globe product out there that uses it to give their offering an edge.