Running a linux Multiseat configuration on Mac Mini hardware
You can do something similar to Linux multiseat configurations with Lion Screen Sharing. If you have multiple user accounts on your Lion machine, you can turn on Screen Sharing in System Preferences>Sharing:



Then, in the sidebar of your Finder window, you can click on the name of your computer, and click "Share Screen". Enter the user id and password for the account you want to log into. If you screen share with a Mac that already has a user logged in, you have the choice use a virtual display, which will allow you to log in to a separate user account.