According to the Nick.com Official Message Boards, there is finally some information on the release date of TLA:LOK. According to the Message Board, Korra is set to come out this Spring! While no concrete date is given, I'm sure that this is as concrete as we'll get from Nick until the Kids' Choice Awards.

BTW, it also calls it Avatar: Legend of Korra and not The Last Airbender, although this could just be allowed for use on the website, since the website is international.

Link

http://www.nick.com/mynick/messageboards/viewboard.jhtml?bID=106921