Yesterday Mojang released the latest snapshot to demonstrate things we could expect from Minecraft's 1.8 update, and it adds even more functions for the use of mapmakers.
Snapshot 14w06a was released and updated later with a b version to fix some more common bugs. It brought very little to the survival side of the game but added ever more commands for the use of mapmakers in the game to use, adding an optional 'outline players' function for spectators, making it so certain types of blocks can only be placed upon other types of blocks in Adventure Mode, a command to prevent item entities from being picked up for a set amount of time and another to stop them from despawning entirely.
However the one survival change talks about a lot of changes being made to the mod AI, which “should mean nothing, but may actually mean something”. To repeat their advice, remember: don't sit on slimes.
Full snapshot notes are here.