Datacenter-in-a-box as a concept has been around for a while. The most popular example of this is Sun's Modular Datacenter S20. This is a 320 rack unit datacenter literally in a box - a shipping container - that can be used for rapid deployment of a datacenter with greater density than a traditional fixed datacenter.
At LinuxWorld 2008 Rackable®Systems showed off their ICE CubeTM Modular Data Center. This has a much higher density than the Sun solution with 28 racks of servers, offering 1400 rack units in all, fitting into a 40' container. The datacenter uses water cooling to reduce costs compared to traditional datacenters. Here are some pictures of the ICE CubeTM: