Number of workspaces in Gnome

Take a look at devil's pie, an app written to allow such customization on GNOME 2.

Note that if/when you move to GNOME 3, things might work very differently…

What I would do, and have done on my in-laws computer, is to open the "Workspace Switcher Preferences" (most easily accessible via the workspace switcher on the panel, before you remove it) and set the "Number of workspaces" to 1.

I don't recall whether this removes the "Move to Right" options etc., but it at least makes them useless. This is good enough for most users, unless you really want to remove all traces of the workspace functionality.