As for XP mode, VMLite auto downloads microsoft vhd file, and configures everything, so user don't need to install Guest additions, configure shared folders, etc.
Usera only need to click a few Next button, then have a working vm.
As for VMlite vm, no other vendor can do this, no iso/cdrom is required, you click a button, a vm will be created and run, same as host os. So you have win7 vm on top of win7 host, xp on xp, vista on vista. VM and host are almost identical except for some hardware drivers. VMLite is the only vm software that can do this.
It's these two features that make vmlite easiest to use.