As I mentioned above, a window manager does not need to be written to support Xinerama. However there are certain enhancements which window manager developers can do to make Xinerama users lives easier. Features which I thought were desireable include:
* Intelligent placement of windows.
- Window managers should not place windows in dead areas or across the borders of two heads.
- New windows should be placed in the current desktop.
* Maximizing windows should maximize the window to the current head only.
* Window Movements should have edge resistance between heads (Much like they have resistance to other windows).
* Dialogs and informative messages should not pop up Between Heads.
In my older howto I had listed a lot of Window Managers and their level of support for Xinerama. But most of that information is obsolete now. Most modern window managers support Xinerama to some extent.