This is going to be for a home server, however I intend on running the following.
RADIUS,
PKI
Wiki Server
Mail
iCal Server
DNS
Resharing NFS Sharepoints via AFP.
Virtual HTPC Mac running ElgatoTV with HDHomerun DVB Tuner.
itunes/elgatotv repository for Virtual HTPC and 2 mini's under TV
Time Machine for MBPro Unibody and 2 mini's.
I believe that going to struggle with this on a mini.
I have been thinking of 3 possible solutions.
1.) 2nd Hand xserve G5 works well with Leopard Server, unsure for Snow Leopard Server but relatively cheap. Not much use afterwards.
2.) Refurb Mac Pro, works well, will work with Snow Leopard but expensive, also wandering about power drain if on 24/7.

3.) EFI-X box running OSX Server, on a DFI board with 45nm Quad Core, 8Gb RAM, 7300GT and Highpoint 3520 and 8 drives for disk controller. Know will work with Leopard Server, and boot from the 3520, also bonjour works on the DFI However will it work with Snow Leopard Server? Also not as nice as a real mac.
Only need the EFI-X box, CPU and motherboard, so cheap. and can reuse the OSX Server software with a genuine Mac if doesn't work out, so only the EFI-X would be wasted.