I've got one of these for testing projects from work at home and got more than I bargained for with the time I've spent on it due to the storage handing/Perc 6/i cards.
My particular model came with the following:
2U Rack Mount Server with Rails
2xOpteron 2373 EE (Quad Core, there is a 6-core version that can be found at times)
16GB RAM
2 x 250GB Seagate SATA
2 x Dell Perc 6/i (horrible and a nightmare to work........
FreeBSD Desktop OSsI would probably choose these over Linux.
In many ways these are probably more stable and just as easy to use as any Linux distros but the benefit of stable, updated and secure packages!
PC-BSD - http://www.pcbsd.org
DesktopBSD - http://www.desktopbsd.net/index.php?id=37
Personally PC-BSD is Beta at this point and is not easy if you are installing it on a non-primary partition.
I have not used Deskt........