I have two - a dual Athlon MP 2000+ system with 2GB of RAM and a couple of 120GB drives giving it 240GB of space - nothing special and due to the fact it's noisy and power hungry I don't bother using it. I would sell it but it's probably worth peanuts so I can't be bothered with the hassle.
My main file server is a P4 2.4 with 1GB RAM and various hard drives giving it around 1TB of space. I just have it running Windows XP - don't need anything flashy on it as it doesn't do much else. I prefer to use XP over Linux largely because of NTFS support with no messing around - I have needed to take the drives out and put them in an enclosure either for lending to friends or because I've needed to take the stuff somewhere and I simply couldn't be bothered to transport the entire box. The only reason it's even as 'good' a PC as it is is because it was spare parts left over from upgrading my girlfriend's PC. Otherwise I would probably have just used a 2GHz Celeron box with 256MB RAM (it's literally running Windows, nothing more, not a single application) for it.
I basically use it for backup purposes. It has a complete backup of my MP3 archive and whatever else I deem important enough to warrant 2 or 3 copies of.
. Maybe i'll put it back to RAID 5.
