If you want the new 1.8 in all it's glory throughout your entire world but also want to save your awesome creations, then just get MCEDIT, save the buildings/areas you want as schematics then import them into the new 1.8 worlds.
I may as well stop playing Minecraft if he gets rid of Survival Mode........
-__- It's still place block, break block, kill scurry monster. It just will be very different with these different features, such as the HUNGER METER, DUNGEONS and NPC villages. I even remember seeing a Tweet by Notch about breaking blocks in the NPC villages. Gawd.
u are all morons, a world is a world is a world, and theres no way it wont work, if u r that woried, just back up your .minecraft, and if it doesnt work, reinstall the backed up .minecraft, and get the illlegal copy of minecraaft.
They don't even need that. It's always been an option to update with the current launcher.