'Facetop' Blends Screen and Video Images
Some UNC researchers have found a really great use for the transparency in the OS X interface. Facetop lets you see a more or less ghostly image of the person you are collaborating with superimposed on the screen. You can see what the person is pointing at, for instance. A Mac version could be ready in a couple of months, but there apparently can't be a Windows version until Longhorn.