Red Hat's Peter Hutterer who originally devised Multi-Pointer X (MPX) for X.Org and other input advancements in recent years was one of the developers (along with Daniel Stone and Chase Douglas) responsible for X Input 2.2 for these improvements. Peter spoke this past weekend in Brussels at FOSDEM 2012 about these input improvements.
While there's already been a lot to read about Multi-Touch / Xi2.2, for those wanting to learn more or find out all of the details in video forum, here's a Phoronix video recording of Peter's X Input 2.2 talk.
Yes, there's also an X.Org multi-touch demo as part of his presentation at the end.
It's still expected that soon the multi-touch improvements will be merged into GTK+ to take advantage of X Input 2.2 within the GNOME desktop.