The code's been checked in, and will go out in the next build is now active on all (non-meta) sites.
What code you ask? Well, we talked this over and decided the problem isn't really jsfiddle it's just super short posts that contain links as the bulk of their content*. Put another way, there are alternatives to jsfiddle that will come to be used in just the same way; so singling out jsfiddle doesn't buy us much.
Instead, we've changed the minimum body length check to not count anything in the form of a link (doesn't matter to what or whether they're even actually anchors when rendered). We'll be keeping an eye on things to see if the minimum length needs to be raised (it's currently at 30, which I think is a little short personally).
So, after watching this for a day and looking at what's getting posted... this wasn't enough. While the length limit helps a bit (and closes some other holes in validation around link-only posts), there were still a number of posts that really should have had code (but didn't) getting posted.
Since we couldn't find a reasonable character limit that looked like it would catch most of the offenders (we had a number of examples > 300 characters within 24 hours), we have started special casing jsfiddle and ideone links.
So, from now on, if you try and post to Stack Overflow with a link to either jsfiddle.net or ideone.com you'll be required to include some properly formatted code as well. We do special case direct links to their home pages, so you can still mention http://jsfiddle.net/.
To be clear, links to jsfiddle and similar services are OK but a question or answer should stand on it'sits own. Enough information should be included in any post to still make it useful for future visitors even if all the links were to break, in other words.
*We've always felt that answers should be able to stand alone, without any external links.