We have a Creative world! To get into the creative world, remove all of your items (armor included) and type "/creative" (I'd prefer not to store - and risk - your entire inventory inside the persistence database). Your health, hunger, and xp will be stored for you. To return to the main world, type "/survival". I've set up a program to run every hour and store a copy of the creative world's dynamic map images for a time-lapse video. I'll figure out how to create the actual video later. Have fun!
Also, don't crash my computer with redstone. If someone does abuse redstone, and I'm able to determine who it was, I'll probably just ban them from using the creative world. If I can't determine who it was, I'll limit it.
Next up, a pvp world or classic-style private mini-worlds.
Edit: Beds cannot be placed in the creative world, and "/invkeep" has been replaced with the boss-reward lives system. If you died before now with invkeep on and never respawned (logged off), your inventory will still be returned to you.