Hi Rake:
The Sandbox term is spot-on, and although I'm not certain of all the hypervisors that offer this feature, I do know that VMware does. There, the feature is called "Snapshot", which allows you to essentially capture the virtual machine at some given point in time. So, if you boot up and do something, then shut down, you can load things back up with the Snapshot instead, which will revert you back to that point in time.
If you want things done automatically, there's also an option to allow you to automatically revert to the snapshot each time you shut down, which is similar functionality to public terminals.
How secure it is in the end game, I'm uncertain. When shutting down, it will wipe out what you just did, but if someone had the skills, they may be able to take your VM file and decrypt certain portions of it, but something like this would require huge talent and in the end, just wouldn't be that reasonable. For utmost security, you might want to write a quick script (batch file in Windows) to automatically "Shrink" the virtual machine's hard disk each night. What that does is purge all of the deleted data in the VM, in order to shrink the physical size of the virtual hard disk, which would result in an absolute deletion of such data.
When I take a more in-depth look at each hypervisor out there, I'll check to see which ones offer similar functionality. But if you are interested in playing around, VMware offers a 30-day trial that you could use.
