I'm a big proponent of using Virtual Machines for development on your local machine. It just doesn't make sense to install things that you don't always need running and consuming resources when you can start a virtual machine (VM), do your work, and shut it down when you're done. Using VMs allows you to develop software against the specific platform you intend to deploy it to and test the deployment to make sure it works. VMs are also great way to try out new software without mucking up your Operating System. I could write an entire post about why using VMs make sense, but I think you get my point.
When Windows 7 came along Microsoft introduced a new version of Virtual PC and XP Mode, a technology which runs a Windows XP VM in the background so older applications can still run on a newer OS. The new version also added support for USB devices - handy if you needed to get data off a thumb drive directly into a VM or use a device that only worked with older versions of Windows. Unfortunately Virtual PC has a major shortcoming in that it only supports 32-bit VMs.
32-bit only support hasn't been a problem since Microsoft has traditionally offered both 32 and 64-bit versions of Windows Server, but then Windows 2008 R2 came along as a 64-bit only OS. That means you can't run Windows 2008 R2 in Virtual PC, and in my opinion that's a major gap in Microsoft's virtualization strategy. I follow Ben Armstrong's (a.k.a. Virtual PC Guy) blog and while he talks a lot about Hyper-V (which does offer 64-bit support) the only recent mentions about Virtual PC deal with running older applications. Between Ben's blog and the lack of Virtual PC updates since Windows 7 was released I can only surmise that Microsoft has reached the end of the road with it's desktop virtualization strategy and if you want to run modern 64-bit OSs in desktop VMs you'll need to look for other solutions. (Disclaimer - I have no inside information about Microsoft's plans here. This is a conclusion I've reached based purely on outside observations!)
Fortunately there are two free alternatives with 64-bit support: VirtualBox and VMWare Player. If you're looking for paid desktop virtualization products there's also Parallels and VMWare Workstation. The paid versions have features that virtualization power users will appreciate, but for most of us the free versions suffice just fine. An added bonus is that all of these support non-Windows operating systems, something that while possible in Virtual PC requires hacks and workarounds to get working even half-right.
I really hope I'm wrong here as I think Virtual PC is sans the 32-bit only support it's not a bad product by any means. However without any plans for 64-bit support announced I will no longer be recommending Virtual PC to anyone who is looking for a desktop virtualization solution.