The default setting for moving windows via Alt + left click + drag conflicts with other applications features and requires the user to modify the default via gconf.

I propose switching the default key to move windows to <Super> + left mouse + drag instead of the traditional Alt key.

Even though the Alt key has been used in Gnome for this purpose for a long time (before the <Super> key was on keyboards, as 'halfline' on #gnome-shell pointed out) I think it makes sense for these reasons:

1) Many other programs (audo editing programs, image editing programs) use Alt + left mouse + drag for interactions, this necessitates a change for users who can't change the applications's keybindings. 

2) Gnome Shell depends on <Super> / mod4 key for many shell interactions, the user must use <Super> to effectively use Gnome Shell, this change seem natural to the workflow of Gnome Shell

3) <Super> + middle mouse + drag resizes the window, so it makes sense that other window interactions should also utilize <Super>

Since Gnome Shell does not support legacy machines, there should be a very low number of keyboards in use that do not have the <Super> key. Gnome Shell is already changing many workflow paradigms, why not this one?