Jon McCann absolutely rocked yesterday explaining how to do a multiuser desktop correctly. I've uploaded his slides here, which you really should read. There's some cool new ideas which makes stuff like gnome-power-manager in a gdm session possible (in a sane way), which we've wanted for ages. But that's trivializing all Jons' work. Seriously, this new stuff will be really cool. Read the PDF.
Dude, keep rocking.