Well, it's more of a collection of boxes doing stuff.
Initially I had a Q6600 box running Windows Vista (indeed!) and had a chance to grab an old box from two jobs ago (basically 5 years ago), an old AMD XP 3500+, running Debian with 2GB
Nowadays the Q6600 runs Kubuntu 12.04, 8GB RAM, GeForce 260 (previous gaming box), and the AMD is still the same, doing same, being file server and basically web server for the bit of (private) web development I do (used to do professional, not anymore), while the Q6600 can run VMs and also SMB shares (store for music and all)
New box is an i7 Ivy Bridge 3770, 32GB RAM, SSD + HDD. Next to gaming it's also there to run VMs (and other hobbies e.g. 3D Rendering).
VMs across boxes I want to use (next to above Web dev) to focus on things I will be doing more at work soon, such as penetration testing, securing / hardening Linux systems, vulnerability scans, exploiting web interfaces, breaking vulnerable packages over the network, play around with log storage from my home machines and servers across a couple providers I use. Next to that any other Linux sysadminy thingy I can think of which looks interesting.
Got three unmanaged switches, two are hand-me-downs 100MBit, the latest finally 1GBit. Looking into sourcing some (older) Cisco switches to start playing more with VLANs around coupled with above stuff.
6 screens to provide full overview of things, top left and center go to the Q6600, top right goes to the laptop docking station (an i5 from work with 8GB for more playing), bottom three go to Win7 box (Mostly though for nVidia surround gaming ;) )
I'd be lost w/o Synergy in cases like this (absolut win of a program)
So it's somewhat a mix a of a "lab" and gaming station. As I'v e mentioned in the previous article which spawned this one, the biggest winner is probably British Gas here...