Purely an anecdote, but the other day I had the occasion to use shred to shred two disks at once. The machine was a modern Intel Core Quad system, and the disks were writing at 60MBytes/sec with 3% CPU load. Since modern shred just writes a number of layers of pure random data from /dev/urandom, I have to assume that there was either hardware crypto or randomness generation going on there. Who knew?!