Client/Agency Engagement is F*cked, Waterfall UX Design is a Symptom | disambiguity
Leisa nails it. The real stumbling block with trying to change the waterfall-esque nature of agency work (of which Clearleft has certainly been guilty) can be summed up in two words: sign off.
And from a client’s perspective, this emphasis on sign-off is completely understandable.
It takes a special kind of client to take the risk and develop the level of trust and integration required to work the way that Mr Popoff-Walker any many, many other inhabitants of agency world would like to work.