They've created a great platform and established no way to make money off it. It is like Twitter in the early days, but like DHH said, it has the disadvantage of being on a thousand different niche websites instead of one aggregate.
One possible way to still make a good return off it is take the Twitter path of getting VC money with the hopes of finding some revenue stream down the road. Maybe they can come up with a similar search deal?
Where do you get the idea that stackoverflow doesn't make money? It appears to make enough money to pay for its own hardware, its bandwidth costs, the salaries of several employees, and more.
You confuse StackOverflow (the company with 3 employees and Joel as a founding partner) and StackExchange (a product of Fog Creek based on the SO code). StackExchange's revenue is less important than the revenue from StackOverflow which is currently derived from ads and the careers site.
One possible way to still make a good return off it is take the Twitter path of getting VC money with the hopes of finding some revenue stream down the road. Maybe they can come up with a similar search deal?