> You need both. Implementation people aren't all that useful without a vision. A vision isn't all that useful without implementation. It's a symbiotic relationship.

37signals' take on this was the best one I've seen (paraphrased):

Ideas are a multiplier. If your execution is good, a good idea will multiply that. If your execution is minimal, a good idea will scrape by. If your execution is abyssal, a good idea will make it worse.

I'd link the actual page in the book, but I have always had trouble finding it.