I'm a single founder with a fairly profitable business (low-mid six figure profits after 1 year). I guess out of ignorance, I never even considered getting a cofounder. I can't say I regret my decision. Having 100% control over the course of my company is something I wouldn't easily give up. In terms of workload, what does a cofounder give you that you can't get for much cheaper with contractors or employees? In terms of emotional support, I think being married actually helps quite a bit. Even though my wife is not actively involved in the company, I bounce ideas off of her all the time.
Perhaps a cofounder is more useful for startups that want to grow very fast (the type YC likes to invest in). But for the organic/bootstrapped style startups (ie 37Signals / FogCreek) is having a cofounder really necessary? Everyone likes to quote PG on this, but consider the source. His experience is with fast growth, VC funded, shoot for the moon style companies. So it may not necessarily apply to everyone's situation.
I'm also a single founder with a fairly profitable organic/bootstrapped style business. Having a supportive wife has been huge for me as well.
I imagine it can feel better to have a cofounder, to feel like you're not in it all alone. But if you want to make something great, there needs to be one person with a vision and the power to make it reality. Nothing really great was ever designed by committee.
Perhaps a cofounder is more useful for startups that want to grow very fast (the type YC likes to invest in). But for the organic/bootstrapped style startups (ie 37Signals / FogCreek) is having a cofounder really necessary? Everyone likes to quote PG on this, but consider the source. His experience is with fast growth, VC funded, shoot for the moon style companies. So it may not necessarily apply to everyone's situation.