It's Grrrrreat!
I have used SME Server for about 2 years. Firstly to replace my router. But I needed a Terminal Services/RDP server and the SME didn't handle port forwarding very well.
So I prefixed a router and had 2 NICs in my desktop - one connected to the router and the other connected to SME. Now I have SME running as a (one of many) VM. The simplicity of setting up email and web servers is so advantageous.
My SOHO network has 2 Fedora 13 servers, a SheevaPlug and UNR 10.04 for the desktop. The RDP server is an XP VM. Although I am considered more than capable technically, I observe Occam's Razor - tend towards simplification.
It results in fewer headaches and one can spend time *using* their gear rather than spending their time configuring it!