Comment 4 for bug 681446

Docky marks some helpers as Usable - other are just hidden from the user (he may optionally show them of course).

Maybe we should just let the plugin define it's 'what do I need to run' criteria? In most cases it would be nothing but in some it may be a presence of some D-Bus object's (like Tomboy) or some kind of dependency (Zeitgeist). This would let us to mark plugins as unusable even before they are initialized.