Linux enthusiasts like to point out just how scalable the system is; Linux runs on everything from pocket-size devices to supercomputers with several thousand processors. What they talk about a little bit less is that, at the high end, the true scalability of the system is limited by the sort of workload which is run. CPU-intensive scientific computing tasks can make good use of very large systems, but database-heavy workloads do not scale nearly as well.
Link: ComputerWorld