There is really no question that a virtual machine is no substitute a native boot environment. However, it sure beats nothing at all if you ask me.

Sit tight, Linux Users. User Mode Linux will soon have the same capabilities as Xen in the virtualization arena — like live migration, says Jeff Dike, author of User Mode Linux. Operating out of the Linux kernel port, UML enables the port to host multiple virtual operating systems.

Speaking with SearchOpenSource.com, Dike described the pros and cons of virtual machines versus virtual operating systems and offers some advice on whether to opt for UML, Xen or VMware.
 Source: searchopensource.techtarget.com