Comment 18 for bug 772177

Hm. This may not matter for Ubuntu anymore, as Oneiric features a completely new Alt-Tab interface.

http://www.jonobacon.org/2011/08/26/ubuntu-11-10-so-far-screenshot-tour/

It looks like it will also be configurable via the Unity pane in CompizConfig Settings Manager.

http://iloveubuntu.net/alttab-ing-gets-automatic-preview-oneiric-ocelot