You all have good points there but the thing that stresses me is that you (like many others these days) do not make difference between an iteration and an increment. The fixed timebox that forces tradeoffs is an increment. A few days ago I tried to illustrate these things, have a look: http://samipoimala.com/it/2010/04/16/iterations-and-increments-explained/ Kanban and other lean techniques are abandoning increments and replacing them with continuous flow of value (and process feedback), but iterations can still coexist if less visible though.