My Windows Vista desktop is also used for gaming, so I kinda have to run Windows on it directly, rather than in a VM. My server used to run Linux, but account federation when dealing with Windows clients was too painful (in fact, it wasn't much less painful with Linux clients), and I had a copy of Windows Server 2003 lying around...

If my server had either Intel-VT or AMD-V (and more memory), I'd probably virtualise more stuff. At the moment, I have two Linux boxes running in VMWare on Windows, but if I could get the federation working (oh, and shared printers), I'd be happy to run Windows Server in VMWare on Linux.

The wife's laptop is Windows XP, partly because I've got about 4 copies not in use, but mainly because of the account federation thing. I'd be happy to try her on Ubuntu otherwise -- she only really uses it for email and browsing.

My primary laptop is Windows Vista, with Visual Studio 2008 installed directly on it -- mainly because it needs quite a lot of memory, and VM disk performance could be better. I do use VMs for some pre-release software (and I'll do this more in future; I just had to rebuild the laptop this weekend, after a SQL Server 2008 RC0 install hosed it).

My web server is a Linux VPS (Debian), hosted somewhere in the US. One of the VMs running at home is responsible for backing this up (using rdiff-backup).

So, I do use virtualisation, but it's Linux-on-Windows, rather than Windows-on-Linux.

Oh, and note that these are all personal licenses (MSDN Professional) for Windows, rather than work licenses, so I can't just go installing a bunch of volume-licensed Windows instances in VMs, which kind of limits my options.

At work, my developer workstation runs Windows 2003 with Visual Studio 2005 and 2008. It runs about half-a-dozen VMs on Microsoft Virtual Server. There's usually a domain controller, a Systems Management Server (or ConfigMgr) box, a SQL Server box, and a variety of Windows clients, all for testing. I'll be installing Windows 2008 on it as soon as I can, so that I can use Hyper-V to speed up the VMs. All of our mission-critical servers (both in IT generally, and development specifically) are virtualised, across two (might be three) large Dell servers. We do this partly for backup/disaster recovery, but also to reduce cost, space needed in the server room, and (in large part) power consumption and A/C requirements.