Check out the news here.
Jonathan Blow hinted at it on his blog, but now it's been confirmed. It will come out on March 31, and it will have Steamworks achievements.

No retail release has been announced. Here's a comment from his blog.

There is no box release at this time. It might happen in the future, and I have talked to a couple of publishers about it, but for the most part retail publishing doesn’t seem worth it for indie developers these days. It’s a huge headache and your game still doesn’t get out to very many people, and then your publisher cheats you and goes out of business anyway.

It's coming out in a week, I totally can't wait.

I KNO!!! Very excited about this!