Just a few days ago, the version alfa 2 of Ubuntu 11.10 was released. This version comes with some interesting changes, may be the most significant of them are the use of the branch 3 of the Linux kernel, as well as the use of Gnome 3.
As you probably already know, multiseat is closely related to display manager, since it is a key component which allows the starting of multiple simultaneous graphical sessions. You probably will know, too, that this feature was removed in gdm (the Gnome Display Manager) in version 2.22. This is the reason why since Ubuntu 9.10 there is no an easy setup to configure a multiseat computer.
In Ubuntu 11.10 LightDM has replaced GDM as the default display manager. This is a rather new display manager, so the first question was whether this new display manager would support a multiseat configuration. The question seems to have been answered and, accordingly to the comments, multiseat configurations will be possible.
We are currently preparing a computer with the alfa 2 of Ubuntu 11.10 just to test the multiseat setup. We will keep you informed about the results on the blog.
Meanwhile, you can have a look to the new features of Ubuntu 11.10