Windows 7RC1, on laptop, and Windows 7 Ultimate (got free for the launch party) on my desktop...
Tho i do keep trying to use linux, but have so much unsupported hardware... It is running on my FriendlyARM Micro2440
One with Win7 RTM (I've bought the production version but haven't installed it yet), one with Vista 64, one with Vista, one with XP Tablet, and two with XP.
On my desk right now I have 2 laptops one 17" Macbook pro running snow leopard with a Vmware Ubuntu image as well and a Toshiba Qosmio running Win7/Ubuntu dual boot. I switch between the two machine for different tasks.