How to disable Finder triangle reveal animation in 10.7 Lion
I've been looking for this solution for quite some time.  What this is is an NSOutlineView.  The expanding and collapsing of an NSOutlineView now always animates the roll down and roll up of the content and makes you wait for it to finish before you can actually see and use the content.  It's infuriatingly irritating that we can not turn this unwanted "feature" off so that it functions as before.

According to a developer at Apple, there is no way to do this and I was encouraged to file a request since this is an annoying addition to the OS that you can not turn of that was not present in previous system releases.

I've reported the bug/usability regression to Apple.  It's bug# 14442959.