Back in 2002, Apple introduced Apple Remote Desktop, which allows for remote administration and management. In 2004, ARD became based upon VNC, the open protocol which meant that the tool allowed you to remotely control not just Macs, but also Windows PCs and other Unix systems with a VNC server installed.
This will now mean remote users can log into a separate user account from the one that is currently logged in, seeing their own desktop and user environment. Previously they would only see what was already on the desktop and there would be a conflict with the other user already logged in for control of the mouse and keyboard.
This will mean that Mac OS X Lion is now capable of multiple, concurrent graphical shells for remote users, somewhat akin to that offered by the technology Citrix created for Microsoft’s Windows NT 3.51 to allow multiple remote users and login sessions.
Although not something that every user will find essential, this will certainly be welcomed by anyone responsible for supporting other users remotely (even if they are at another desk locally).