Very cool. The guys over at codeweavers have begun porting their excellent wine-based system for running windows apps seamlessly under Linux, to mac. Currently it requires X11, but they are working to remove this dependancy.
What this means is that there would be a potential for being able to click on a .xls file on your Mac-Intel desktop and have the windows version of Excel launch. Ok, maybe a bad example as office is available for Mac. A better example is Half Life 2, which is being worked on by codeweavers devs :)