This bug is also being discussed at http://blogs.gnome.org/metacity/2009/01/25/squib-of-the-day-live-previews-in-alt-tab/ .

Setting this to be blocked by bug 504729 given bug 504729 comment 10.

While having the functionality in the Alt-Tab window is not useful per se, having this implemented would open new possibilities for exposé-like applications, and a workspace switcher that can display more than a gray area (with an icon, but only if it fits).

In any case the discussion about it being useful or not is pointless. One should have the ability to choose on their own if they want it or not and it should just be configurable and that's it. There's no point in fearing the implementation just because of fearing new bugs in my humble opinion. Right now we have ugly looking bigger-scaled icon images which just look very bad, which you can't even set to be original-sized, a big mess if you ask me... One could switch off Compiz but i don't think of it being a solution just to get a decent alt-tab switcher. Then again the minimize-animation is annoying which you only could switch off while getting rid of opaque window movement too... I just think we shouldn't take the freedom of choice out of gnome for no reason.