Vista still uses a two-ring user/supervisor split, and so will operating systems yet to come. Virtualization software like vmware have used the other rings because virtualization is tricky, but with the VMX (Vanderpool/Pacifica) instruction sets, my bet is ring 1 and 2 will be used even less.
Btw, I sent the vcblog team a mail asking about the exception handling stuff, and they said my questions might be answered here (haven’t had time to watch yet, though): http://channel9.msdn.com/Showpost.aspx?postid=343189