I recommend getting a copy of the original Don't Starve as soon as possible if you're planning on buying the future multiplayer version. This is because the developers are planning on giving away the multiplayer expansion for free to those who own the single player game before the multiplayer alpha comes out. Forum Post Here
Multiplayer being worked into Don't Starve will be a hell of a lot of work for the devs. Still...good news as I own the game already