I just ordered one - NO affiliation with HP or any vendors - just a nerd who likes bargains.
A dual core Athlon 1.3GHz (so can do H/W virtualisation, better than Atom performance) based micro server, with 4 drive bays, apparently nearly silent...
http://blog.samat.org/2010/12/10/Har...6L-Microserver
I found using Google shopping the basic config for £199.99 and if invoiced before end of Feb then HP will give you £100 cashback...
http://h41112.www4.hp.com/promo/prol...antmicroserver
Bargain!
Upgrade with any DDR3 RAM and regular 3.5" drives, server includes a full set of drive trays. I reckon that's full of win for a home server, NAS or test box.