Seems Microsoft are going for it too . . . or maybe this is just for the menus . . .
http://www.bentuser.com/article.aspx?ID=332&
Folders toggle open and closed with a single click. When I first heard about this, it sounded like a horrible idea. But after actually using it, I can say that it is actually a significant improvement over the dreaded 3-column-wide All Programs list from XP.