Seen them in operation already (Score 2, Informative)

Japan's TSUBAME (see the system at http://www.gsic.titech.ac.jp/) is made up of both x4500 and x4600 systems. I've been in the Thumper room - it's loud as a jet engine in there and cooling is an issue, but only because the room is old. It's an impressive set-up, and made to be upgraded. They've got 1.1 Petabytes of storage now.