Returnil Virtual System is an interesting compliment to your PC's security system, but it's not glitch-free.
The software creates a new partition on your system's hard drive, and then mirrors it. It acts as an isolated work environment that protects your actual system by preventing downloads and such from accessing it. Instead, anything created in this pocket of your drive--this virtual partition--is erased when you reboot. Since toggling the protection requires a reboot, Returnil isn't as simple as running a basic DOS shell. This is a minor speed bump if you're working with potentially destructive software or visiting Web sites that may attempt to load malicious software, but it certainly slows productivity.
The utility adds an icon to the system tray and a small Returnil bar, always on top, near the top of the monitor screen. Clicking the bar lets you configure settings and open or close the virtual partition. Returnil does have some kinks to work out. When booting up, Windows Explorer would shut down and relaunch, slowing the entire launch cycle. Also, make sure you've got pop-ups disabled in your browser because they forced a crash when launching over Returnil. Generally, though, Returnil works well as an isolated and safe sandbox to play in.