A Phoronix reader pointed out a new 40 Raspberry Pi Cluster built by David Guill. With 40 Raspberry Pi boards that amounts to 40 Broadcom BCM2835 700MHz cores, 20GB of RAM, 5TB of disk storage, about 440GB of flash storage, and 10/100 Ethernet. The approximate system cost of the full build was $3,000 USD.
Most interesting out of this Raspberry Pi cluster is the meticulous assembly and organization of all the Raspberry Pi ARM development boards inside a custom-built acrylic chassis. Those interested in checking out the experimental Raspberry Pi system can find details and pictures at LikeMagicAppears.com. Some YouTube videos are also embedded below.
In the past at Phoronix we have dabbled with some ARM clusters but in the end the performance doesn't tend to be too good due to most ARM development boards being limited to 10/100 Ethernet (and only now seeing more Gigabit Ethernet) and poor disk I/O (but at least now there's more ARM boards with Serial ATA). The Raspberry Pi performance overall is quite poor and not too exciting even at a scale of 40 boards, besides the lower-cost compared to other ARM development platforms. If you are interested in this kind of stuff, checkout our building a 96-core ARM Ubuntu super-computer and the former 12-core PandaBoard ES cluster. On Phoronix you can find many ARM Cortex Linux benchmarks and via OpenBenchmarking.org with the Phoronix Test Suite having full ARM Linux support.