Hutchison made the necessary changes to the Android software stack, and also wrote a number of demo applications to show off the multitouch capabilities of Android and the G1. Note, though, that this is a proof-of-concept, and that performance isn't up-to-speed due to the lack of OpenGL acceleration and the lack of kinetic zooming (should be "trivial to implement", he adds). Hutchison also explains that the current API only implements step-wise zooming, taking the fluency out of the animations.
The implementation is completely forwards and backwards compatible; you can implement extra multitouch features into your applications, without breaking them for unpatched G1s:
The remainder of the blog entry deals with how to patch your G1, which obviously comes down to flashing it with a community firmware. According to Hutchison, it is unlikely that multitouch support will ever make it to the G1 officially, despite the fact that there is support for it in the Android kernel. "In my opinion, it is unlikely that the G1 will ever get official support for multi-touch from Google in its lifetime, because it was never designed as a multi-touch device, and there are some limitations to multi-touch on this device," he explains, "Google will also not accept upstream this specific workaround solution to hack multi-touch onto the G1, understanably so, as no multi-touch API has yet been proposed or agreed on. See this thread for more information."