In joint work with Maxim Kontsevich we suggest an approach to the count of stable objects in a 3d Calabi-Yau category based on the ideas of motivic integration and derived algebraic geometry. As a corollary we obtain a wall-crossing formula for the corresponding invariants. I plan to discuss this circle of ideas as well as the relationship of our approach to certain birational symplectic automorphisms of tori (cluster transformations).