So, if you haven't already heard, Jeb sneakily leaked 1.8 the night before last after he had to keep delaying it. It's quite buggy, and it only comes as a .jar with which you replace your own .jar in the appdata folder, but if you want to help playtest for the last few days before its official release, I think Jeb posted a link on his Twitter page.

Buggy but amazing.