Nested quotes would be really cool. I was just reading a thread in TechOff and it went like this: user A wrote a post, user B replied with "+1", user C replied to user B with "Also +1", but when you read user C's post and you expand the "In reply to"-section, you can just see user B's post and you don't know what he replied to.
Ah, yes, that would be cool. Might take some work and we've got other bigger issues on our list, but I like it. Will think about it.