Which companies out there addopted Basecamp's ShapeUp?

I'm reading ShapeUp and what's described there sounds awesome. 6 weeks work + 2 weeks cooldown. Well prepared (shaped) ideas, design work highly integrated (instead of handed over to devs to implement). Small teams of 2 devs + 1 designer. Feels like very energetic place to work.

Sounds too good to be true. Are you working in a company that adopted it and could share your experience?