The best case scenario is to find someone when the idea is in its nascent stages. That way the product can be developed with the market and consumer in mind, specifically how it's going to get to the consumer. Tweaks can be made along the way so the the product has a more perfect market fit. Then marketing is easier because, with that person on board, ideally lots pf testing has been done to see if the product ideally fits the marketplace's demand. If consumers don't really want it, then no amount of marketing will help them to buy it. And rarely does creating a fully birthed product and only then thinking, "Ok, now who wants to buy this and how do we get it to them?" ever work.

I say, find someone non-technical or someone who focuses on this from the beginning as a co-founder. Having all hackers means sometimes people can get lost in the trees of coding without even remembering what forrest they're in. Tons and tons of exceptions to this rule obviously but certainly what I've seen. Also, it's much tougher to bring a product to a marketing person that hasn't been throughly market tested and tweaked thereof, and simply say, "Ok, now you do the rest." The market and consumers should always, always be in anyone's mind the entire time they're creating a product.

Also. There are tons of non-technical types with wealths of experience in business, marketing, etc etc. on HN. I being one of them :) Hell, I think it's near impossible to find programmers since I don't run in programmer/hacker circles. So we always have the same question of where the hell do you find a great, technical co-founder who's a compliment to yourself. It's all a bit like dating I suppose.....