Being shown off publicly for the first time today is a 48 node, 192-core Calxeda ARM server in a 2U form factor. This Calxeda setup has integrated SATA for disk storage. Each Calxeda node is running under five Watts. There's support with this Calxeda configuration for up to 1,000 nodes per rack and some partners doing even denser configurations. This Calxeda ARM hardware is already running on Ubuntu 12.04 LTS.
By later this summer Calxeda is talking about the possibility of a public cloud on this large ARM server configuration. Reportedly later this month they'll be shipping their first ARM server to Canonical.
More details are forthcoming from UDS-Q in Oakland.