Rober X. Cringely from PBS speculates on what Google is planning to do what all that dark fiber they have been buying up. He basically says Google is aiming to own Web 2.0:
The probable answer lies in one of Google's underground parking garages in Mountain View. There, in a secret area off-limits even to regular GoogleFolk, is a shipping container. But it isn't just any shipping container. This shipping container is a prototype data center. Google hired a pair of very bright industrial designers to figure out how to cram the greatest number of CPUs, the most storage, memory and power support into a 20- or 40-foot box. We're talking about 5000 Opteron processors and 3.5 petabytes of disk storage that can be dropped-off overnight by a tractor-trailer rig. The idea is to plant one of these puppies anywhere Google owns access to fiber, basically turning the entire Internet into a giant processing and storage grid.Read on over here.
While Google could put these containers anywhere, it makes the most sense to place them at Internet peering points, of which there are about 300 worldwide.