From the developer's blog:
"Seriously, it's been killing us to keep all the news about N+ quiet. We have really big mouths, and it's hard to shut that down. But, finally, we're FINALLY allowed to share the good news with everyone. N+ will be available for download for 800 points on this Wednesday, February 20th, at 9am PST. Yay! We feel like maybe there's not as much buzz as there could have been, but the orders to keep it all under our collective hat came from Microsoft's marketing department, and presumably they know a lot more about this sort of thing than we do."