Wired:

In an exclusive interview with WIRED, Federighi said the frameworks for porting iPhone and iPad apps to the Mac have been in development for two years. He revealed some of the technical details around how this will work, and shared some of the types of iOS apps he believes make sense on the Mac.

There are some developers really excited by this and others who are really unhappy about it. Regardless, it will be interesting to see what this brings Mac users in the future.