I like the idea of being able to quickly have a full OS and environment available for use through the distribution of files for a virtual machine. Especially with the cost of VM software driving down quickly (for personal use without support this is now usually free), this is especially useful for development and testing.
A couple quick links on this:
- rBuilder Online - Release: LAMP appliance (I found the latest release to be broken, but this one works - your results may vary)
- Orcas Community Technology Preview. Next generation Visual Studio on a virtual machine - no need to risk pre-production software on a machine you care about.
- Windows XP with IE6 or IE7. Great tool for testing
- Directory of user-contributed VMWare images for a variety of purposes