A decade ago, I was an executive at an Internet startup named Mercata. Mercata was one of a couple of entrants in a field we had named "group buying." In practice, this meant there were limited time sales where the price of a product would fall based on the number of people who agreed to buy. Obviously the volumes were not large enough to get economies of scale of any sort, so they main advantage of the approach was viral marketing -- once you had agreed to buy, you had an incentive to get others to join in as more buyers would reduce your price.
The company eventually folded. The company was very professionally run for an Internet startup of the day, but it had a lot of overhead for its volume, and, as eBay would learn, a lot of people wanted to buy immediately rather than wait for some sort of auction to play out.
But it turns out that one of our biggest failures was timing. Recently, a company called Groupon has taken advantage of social networking that did not exist 10 years ago and has been quite succesful building a business using a very similar model to Mercata's. It appears that Google has just bought Groupon for $2.5 billion. Sigh.
This is not, however, even my largest financial missed opportunity. I still have in my desk a 1984 job offer from Microsoft, which I eschewed at the time because it paid less than my other offers and tried to compensate me in these crazy pieces of paper called "options." I once calculated the current value of the options just in the offer letter (ie not including any future grants over time) and their value was well north of any conceivable net worth I might reach currently.