It goes beyond just identifying the opportunity though. The way we run Endcrawl is heavily influenced by Pliny's experience running OFFHOLLYWOOD, a post-production facility that mostly served indie filmmakers. Left to my own devices, would I have nailed pricing (flat fee, no room for bargaining) and customer support (email-only but responsive) like we have? Doubt it.
Hackers take note: non-technical co-founders CAN bring a ton of value to a partnership.
Or: if you're going solo, make sure you really understand your customers and your industry.