Here's the latest on a new HP data warehousing appliance that "will scale out to hundreds of processors and hundreds of terabytes of data," according to a recent CIO.com article.
Apparently, the NeoView server is already in the hands of beta testers and will be officially announced within the year. The max configuration is 256 Itanium 2s across 23 cabinets.
The only drawback seems to be the size. A single cabinet holds 42 rack units, and a fully configured 256-node system requires 23 cabinets. Plus you'll need the HP ProCurve 2848 switch to tie it all to the LAN and then up to eight GbE links to the provider network.