as the title suggests im just curious to see what OS people are using and what configurations your running in/under…
I’m using the LTS versions of Ubuntu Server, currently 10.04. Hardware platform is virtual machines under VMWare ESXi 4.1.
Can you specify what you mean with “configuration”? 
2x dedicated server centos 5.6 - mostly default installation
1x VMWare machine I have 1 Ubuntu LTS 10.04 - default installation
QNAP TS-239 Running Ubuntu 11.04 Server
Webmin 1.550
Virtualmin 3.86 GPL
CPU load averages
0.08 (1 min) 0.12 (5 mins) 0.13 (15 mins)