High Performance Computing

I am interested in setting up some High Performance Computing clusters and would like to get people's views and experiences on this.

I have 2 requirements:

1. Compute clusters to do fast cpu intensive computations
2. Storage clusters of parallel and extendable filesystems spread across many nodes

Both of these should run across multiple commodity hardware nodes and ideally be Linux/Unix based and open source.

Any feedback welcome.

Have you read this:
DistroWatch.com: Put the fun back into computing. Use Linux, BSD.
There is one review to one of them, which may prove helpful. Otherwise check with the RedHat users, as RedHat is often used in HPC enviroments.