Charlie from The Inquirer claims Intel will ship out its first Larrabee boards to developers in November.
Before you get your hopes up, these are not consumer parts, nor were they meant to be. Dev means developer, and chances are the epic MMO that you are whipping up in your mom's basement does not qualify.
The initial boards are meant to code against, and they will do that nicely. They will not be at the final clock, final core counts, or final anything however. If you want to get your feet wet, Intel should have a board for you in a few months.
Don't expect stunning performance though, Larrabee is a new paradigm, and that takes a long time for most devs to wrap their brains around. If you are just going to code DXxx or OpenGL, you don't need one of these.