"What's wrong with having one founder? To start with, it's a vote of no confidence. It probably means the founder couldn't talk any of his friends into starting the company with him. That's pretty alarming, because his friends are the ones who know him best."
Someone else mentioned it on this thread, but I'll expound. The majority of good solid people who are capable of being 'co-founders' of something are likely already doing it. 'Capable' has many dimensions - financial stability, personal drive, motivation, risk tolerance, etc. This notion of 'get your friends to join you' is extremely narrow, and while this may be how life in the Valley is, I can assure you it's not like that in most of the country where the rest of us live.
Also: "And you learn a lot more about yourself and your limits." That's right. One of the things that happens with 'co-founder' situations is that you're both learning about yourselves and each other at the same time. Taking on a 'co-founder' who's "good with sales" - unless there's a demonstrable (and ideally long) track record is essentially a huge gamble, as both of you are making a guess about someone's ability. Personally, I tend to discount anyone's self-estimate about their own ability - show me the track record.
As for the other comment about 'only being able to do so much on your own' - that's what hiring other people is all about. I understand there's not always money up front to do that. But I'd say you'll be in a much better position to contract out the bits you can't do, either at a reduced rate or some sort of time-limited profit sharing, but in no way just bring someone on as a 'co-founder'. If they are truly starting at the beginning, that's different, but bringing someone on after you've done much of the hard work - nope. Yes, you might not be able to find quality talent, but you couldn't find it in the beginning anyway.
My own view is I'd be much more likely to want to work with someone after they've demonstrated the ability to do something on their own which produces revenue (or something insanely innovative from a technology viewpoint that I grok instantly and see a distinct vision for, but that's not crossed my path yet). If you've got 'a cool idea', and want me to come on board as a 'co-founder' and do all the hard tech work, and you've never sold anything to anyone, and want to veto every suggestion I have, we're not co-founders - you're looking for hired help. And that's fine, but the hired help need to be paid.
I've been approached numerous times over the past few years about coming on as a 'technical cofounder'. Only once did someone even have a proof of concept put together that was demonstrating the idea in rough form (including a revenue stream, however meager it was). In all other cases, the execution onus is entirely on me, and in every case, there were some rather odd directions people wanted to move in. When questioned, in every case the 'founder' (who hadn't done anything except float an idea by people) was adamant that the vision was great and couldn't be changed. And without me (or someone) it couldn't be executed, but that point seemed to be lost. It seemed people I was talking to would generally rather have 100% control of an idea rather than, say, 80% control over an actual working service/product. Maybe my experiences are radically different from others who get approached about being 'co-founders'?
Short view - I agree with the notion of 'DIY' as far as you can as a single founder in your enterprise before you start looking for help. With the luxury of some initial success behind you, you'll be in a much better bargaining position when bringing help on board in whatever capacity (paid, equity, etc).