I've recently been testing OSX Lion and I've been trying to use the multiuser VNC functionality. However, when I try logging in the TightVNC or COTVNC, I'm presented with a list of users (including the currently locally logged in user) but I'm unable to select a user to log in as (i.e. click on the user icon/name) has no effect. Are Apple forcing us to use ARD or must we be running Lion on the remote machine to log in too?
It looks like a bug in their new implementation of features into VNC. I just tried with RealVNC viewer and Chicken of the VNC. Since it claims to be implementing VNC, I submitted a Radar, mirrored on OpenRadar.
(I don't believe this is a violation of the NDA as I'm not revealing any new features.)
Also, you should check out AskDifferent.com, the Apple StackExchange. There's a lot more of "us" there than here.
This is a new feature of the ARD protocol, as implemented in Screen Sharing.app. I'm not sure that it's going to work in other VNC clients unless they use the ARD protocol (which I thought was proprietary.)