I went by the Georgetown Coop tonight. I'd say only about 25% of the brands are on sale, and only some of the pieces of those. The ones I remember are Theory, Surface to Air, Marc New York, Penguin and the Barney's house brand. Standard markdown was 40%.
Most of the best stuff wasn't on sale (APC, Nudie, Rag & Bone, NSF, Paul Smith, etc.)
They are putting markdowns on the tags. So, it may be "private," but it's no secret.
Overall, pretty underwhleming.