Nice idea.
It doesn't fully work yet though.
Quotes prior to the hack, are still old style (granted that's probably because of post cache in html).
When a user makes a post with a single quote in a topic and then another post with a single quote, only the first one can be un/collapsed. The second one is uncollapsed from the start and can't be collapsed. Even worse, collapsing it just collapses the quote in the first post.
http://forums.totalwar.org/colquote.gif
Quotes from different users work fine, as long as they are the first one by that user.