The Haiku window manager does exactly this, but it also resizes the viewport such that the scrollbars are always visible. I've always thought it would be a great feature in other stacking window managers.
The BeOS (and therefore Haiku) window managers were well beyond their time. The tab style is still my favourite windowing paradigm.
Seriously, everything should have tabs.
Everything does have tabs. All your windows are just tabs on the task bar!
I have never used Haiku myself, but that is exactly what I was thinking while playing with this example. Did Haiku 'remember' the original size so that it bounced back as you dragged it away from the edge?
Yes it does. As you drag it back from the edge it returns to its 'desired size' (the user's last explicit resize).