OpenBSD 4.2/amd64
I've installed 4.2-RELEASE, upgraded from 4.2-RELEASE to 4.2-CURRENT, then I wiped that install and re-installed 4.2-CURRENT.
The hardware support is phenomenal. The only device that does not fully operate out of the box is the wireless card, which is currently under development. (Broadcom 43xx series 802.11b/g)
Xorg worked without even needing a conf file. I'm using Xfce, and was able to get OpenOffice, Pidgin w/Audio, and XMMS installed. The only problem is, the original purpose of the box was to at the very least, dual boot. I ultimately (at this point anyways) ended up backing up the BSD install to a dump file, and re-installing Windows XP on a partial slice of the HD. In the future I may bring OpenBSD back as a VM until I am able to fully perform all of the tasks that I need to under OpenBSD natively.
At some point in the future, my goal is to clean up this page.