Look at some of the customer development stuff that's come up recently, though; I've seen companies with very very little actual code/product (in some cases, none!) iterate extremely quickly through wizard-of-oz smokescreens and the like.

I agree that fast execution and the ability to turn around and change what you've done (some hackers I know are very change-resistant, note) is important - that's why my last startup didn't do as well as it could. But a lot of that could have been saved with more customer-development methods as well as faster, better code.