Well, I'm am old man at almost 40 and I've spent the last 18 years working for startups of less than 100 people, many of them successful, and almost all of them founded by more than one person-- and in almost all situations I knew at least one of the founders very well.
The number one thing that caused the unsuccessful companies to fail was fights between the co-founders. And the successful ones-- were ones where the co-founders were very harmonious, because they had worked together for years before founding the company (multiple instances of this.) Of course, there were also instances where co-founders had worked before and they still fought all the time.
A co-founder is not what you need, unless you already have one, and you have as good a relationship with them as the best relationship you've ever had with anyone in your life. If you KNOW you're not going to have a problem, then great.
But for most of you-- those who don't know others who are as entreprenurial or don't already know someone - and have known for quite awhile that they would be a good co-founder-- you should not get a cofounder.
I know that PG says you need a co-founder, but while his intentions are good he's slightly off the mark. Sure, its better to have more than one person in the company... and feel free to call your second thru fourth employees "co-founders" or give them "founders stock"... whatever.
But at the end of the day, if its your idea and you are the one who has decided to dedicate the next several years of your life to this project, then found the company and make everyone else who joins you an employee.
Employees can have good chunks of stock. But you gotta have the authority question out of the way. You have to be a good leader to run a company... and getting people in you don't know too well works much better when you both know they are employees (Even if they are called founders or whatever, how about "founding team" or "founding employees".)
Its better for you to have the ultimate say and make a few wrong decisions, than for you and your co-founders to be fighting.
Nobody will ever have as much passion for the idea than the originator, and genuinely visionary people understand their idea on a level and in a context that nobody else will ever... thus you have to lead.
Next to Venture Capitalist (who force companies to misallocate funds or go after longshots and abandon sure things), co-founders are the biggest reason companies fail. And actually its even worse- when you have co-founders VCs like to get involved and start manipulating things.
Every time I've seen one founder pushed out or marginalized in favor of other founders by the VC firm, the company has not lasted 9 months after that.
For an example of the success of a single founder with founderr employees--look at Amazon.com. Bezos is clearly the founder, and he got engineers in early, they got good stock, but they knew what they were. The company would be much different if these employees had thought they were equal with the guy who had the vision.
So, those who are desperately seeking a co-founder.... stop... employees are much easier to find anyway. And you can find ones who will take stock as compensation. (Just don't be stingy-- I once was in talks with a company who was building out the founding team and offered me %1 stock plus a serious pay cut... I turned them down-- why take the real risk of a pay cut when there's no equity upside?)
Anyway... think about it-- and don't be held up waiting for that founder... start pressing forward without one and when you need to build your team, bring people on who are ready to follow you... and when their egos are not involved, things will go much better.