This is one of Joel's well-known assertions, it's even step #9 in the Joel Test and the classic view is nicely illustrated here:
However as part of considering this, I wondered if a counter-claim is at all reasonable. After all, most of the time writing complicated software is done away from writing code. Wouldn't a great developer use the time spent compiling to be planning his next steps, even using the time to mentally regroup? I don't mean to say a slower PC would increase productivity, only that perhaps it shouldn't decrease it for focused, awesome developers who make every minute count.
I'm more than happy to be convinced the answer is no, I'm playing devil's advocate more than anything, but please use reasoned arguments rather than automatically dismissing the idea because Joel said it, etc.