Ebay has admitted what equity analysts have long known - that it paid over the odds for Skype. I reckon there are three general lessons to be learned here:
1. Innovative companies don't often make money. As William Nordhaus showed (pdf), the benefits of innovation flow to consumers, not shareholders. Instead, firms make money by having the power to exclude rivals and kill competition. And Skype can't do this. Not only are there lots of competing Voip systems, but it's also hard to compete against cheap call charges in the US.
2. Synergies are over-rated, diseconomies of scale are under-rated. Ebay hoped that Skype would somehow drive traffic to its auction business. This never happened.
This corroborates one of the messages of this paper (pdf) - that mergers work best when they aim to cut costs, rather than raise revenues through synergies; remember AOL-Time Warner?
3. The price elasticity of demand is very high between a free service and a paid-for one. If you try charging customers for something they can get for free, they'll often leave. Just ask the FT or New York Times. This is entirely consistent with this; once you charge for something, you break the norm of reciprocity, and signal to customers that we're in the realm of homo economicus, so they act accordingly.