A pre-release version of 1.8 has leaked
. I'm a little wary since the source is 4chan, but it looks like it comes from Minecraft's own server and plenty of people have tried it and are saying it's legit. It's possible that it was intentionally leaked as Jeb wanted to release a beta version of it this evening for "advanced users" but couldn't as there was some major bug he couldn't fix on time.
I downloaded the jar file just in case the link gets taken down later and I'm considering trying it out on my laptop.