I just noticed this on Stack Overflow.
I can't find any mention of it in the Recent feature changes to Stack Exchange.
I don't know how this will work out on the other Stack Exchange sites, but this is a horrible idea for Stack Overflow - quotes have semantics! This will completely kill the ability to copy and paste code. See this question for example:
Update: it appears that this is not a feature in the body text but it is for question titles, which led to some confusion on my part. Does anybody know how long titles have been like this?