Hellooo, this is Coock! i'm telling you today, about a secert. on the minecraft forums. Notch Leaked 1.8!!!

Here is link: http://www.minecraftforum.net/topic/611468-want-to-play-18-early-heres-how/page__st__2020__gopid__8216591#entry8216591

just delete old jar file and bring in the one you downloaded! Have Fun! (course you will!)

Just a word of warning, some things are not in yet. (NPC Villages, Mobs running away, etc)
but, i might be wrong, just look around the world! in the new creative mode, ive discovered, exposed stone, EPIC MOUTAINS (im actully, HUGE HILLS.) and little caves IN the mountains. please post here if you discover more things i diddnt get. So thats all i have to tell you, just getting it out.