"I know that "no specs" is very big right now, with high-profile designers insisting that you don't need to do any kind of documenting or specs, that you just need to make a few sketches and then start writing HTML prototypes, re-writing it until the customer likes it. This sounds suspiciously like the code-and-fix model, which we all know is garbage. Even worse, it sounds like undisciplined, hippy-dippy, egocentric, "I am an artiste" thinking. In fact, I dare say that it is non-design. For God's sake, people, we're in a pseudo-engineering profession. Act like it. Plan your work ahead of time, at least the important parts of it."

http://www.christopherhawkins.com

I'd also add that the no spec folks tend to generally be talking about in house projects with very small teams. I've done no spec work with consulting clients and it's a total nightmare.