Often when I opened the spaces-overview rapidly in succession I noticed that windows were consolidated in my current space. I always considered this a bug, but now I'm starting to doubt it.
If you rapidly press the Spaces button four times all your windows will be on your current active space. Apparently you can then select any of these windows and do what you want with them, e.g. resize them, hide them.
Afterwards if you press the Spaces button again, all of your windows will be at their original location, but any changes will still be executed. Unfortunately Exposé to view all windows won't work.
Whether this has any practical use is of course a different question, if anyone has suggestions, please do comment.
[crarko adds: I have a tough time reproducing this. I'm pretty sure this is a designed behavior of Spaces for doing window management, but can't be sure either.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20110131083114909