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.
Those slides come out totally unreadable to me: bright yellow font on a white background or something? I'm using evince something-or-other.