A new set of patches have been published by Benjamin Tissoires that provide preliminary support for multi-touch within the X.Org evdev driver. The patches can be found here, but of course you need a multi-touch device for it to work.
While these patches have been worked on for a while by Tissoires, Carlos Garnacho has today announced another approach to multi-touch handling. In his lengthy mailing list message he describes what he views as the problems with the current EvDev implementation and how it could impair multi-touch adoption on Linux. With his proposal, Carlos also has a branch of the xf86-input-evdev driver that has his changed code along with a small patch that goes against GTK+ to work more according to his ideal way with multi-touch support.
Nothing is yet committed to the mainline code-bases, but we'll be monitoring the situation to see how multi-touch support evolves.