A serious question for hackers or would-be hackers. I think the most serious barrier to many start-ups ever getting started up is the would-be founder who knows better than to go solo, but who isn't sure how to find a suitable co-founder. What do you suggest for finding a co-founder?
I talked to an old guy that ran a large trucking company some years back, and based on his own experience he gave me the following advice: Never start a business with people that have the same qualifications and interests as yourself. He had once started an unsuccessful trucking company with three other trucking people. The result was that they had amazing trucks that were always in perfect shape, but sales, marketing, finance, and all sorts of other things didn't get done. And they failed. His current company was started with an accountant. So try to find a partner that finds the stuff you're uninterested in interesting.
That said, finding a co-founder is hard - you don't know whether it'll work out before you'e tried it. So the best advice is probably to test each other out, maybe by doing a small project first, and seeing how it goes. Additionally you should have a written agrement on what happens if it doesn't work out.
And most important of all: Don't take it personally.
Track record. What have they produced in the past? Do they tend to complete things they've worked, or die 90% of the way to the finish line (a really bad thing)?
Have they had any fallouts/meltdowns? There will always be a "good reason" it happened. No one will say "Yeah, I was a prick, and a drag, and a pessimist, and the company/project/whatever collapsed largely because of me." Also beware the, "I was immature back then, but I've recognized what I did wrong, and I've improved." No they haven't. At least, not if their last gig was a failing.
Past a certain age, the vast majority of people pretty much don't change very much at all, ever. And if they had changed, they'd have accomplished something they could show you. So look at track record - it doesn't lie.
Beyond that, there's plenty of good advice and Paul Graham's written on this plenty. A very big one for me - do they read books? Yes, books, not blogs/social news/newspaper/magazines. Avid reader of books is always a huge plus. Knowledge and lessons from books are repeated into you many times over a few days to a couple months as you read, so it sticks more permanently than reading a smorgasbord of unrelated things.
That said, finding a co-founder is hard - you don't know whether it'll work out before you'e tried it. So the best advice is probably to test each other out, maybe by doing a small project first, and seeing how it goes. Additionally you should have a written agrement on what happens if it doesn't work out.
And most important of all: Don't take it personally.