One of the advantages of KDE is that there is consistent functionality for switching users. No matter where one clicks on "switch user", the behavior is the same---including always displaying a list of users already logged in.

I have made various attempts to get similar functionality in the "light" desktops--eg XFCE and Fluxbox. The most common solution involves the use of GDM + gnome-screensaver. I have not yet been able to get anything as polished as in KDE.

What seems to be lacking is a login manager (like GDM), which has the screen-locking built-in (I don't really care about having a screensaver--I use them only for the screen-locking). Again, the idea is to get seamless operation of user switching regardless of whether the command comes from a running session or one that has been locked.

Anyone have any ideas or comments?

I am not too sure about what exactly do you miss outside kde.

However, I know that xscreensaver can use gdm as a backend to do new logins from a locked screensaver. Not all distros might have that enabled though, since compiling xscreensaver with that option enabled means that xscreensaver has gnome as a dependency. A bit scary if you ask me.

In KDE, the "switch user" functionality and user interface is the same regardless of whether accessed from a running or locked session. I cannot duplicate that in XFCE or Fluxbox. for example, using XFCE and GDM, I have the following:
If accessed from a running session, I can choose another previously opened session.
If accessed from a locked session, I get the GDM login dialog. After logging in there, I must then again log into the locked session.

Maybe this is simply the unavoidable consequence of the fact that XFCE, Fluxbox, and others depend on someone else's login manager and screen locker.

I see.

It's hard to tell 'cause I have none of them installed (I just login from text console).

The main support must be in the login manager. So, if kdm supports it, nothing stops you from running kdm instead of gdm. However if xfce and fluxbox have no way to contact it, then it will be a hard thing to achieve. It might require some patching.

I guess that kde, to do this, might communicate with the session manager (ksmserver) using dcop, however, ksmserver can't be run standalone (or at least, I never managed to do so with success), unless you run kdeinit, which is mostly the same than running the whole kde.

If this is doable using gdm, there might be a way to control gdm or launch it via shell scripting. If that's doable (I have no idea) then you might be able to find an universal solution that you could use on all the WM's. But I know nothing about gdm.

I am going off topic. All in all, I can't help, sorry.

There shouldn't be any reason why this can't be done in any other WM or desktop, using what [gk]dm provides. It's just a matter of coding it, but I don't know if there's already any support on any desktop or WM.