One thing that has kept us from using APIs is that there isn't an established business model, other than amazon.com affiliate links, which is a sucky business model. Almost all public APIs are free to use for non commercial purposes or for a limited number of requests. But, there is no public pricing if you want to build a commercial application off of APIs. And there are no obvious "contact me" forms, either. In other words, there are very few companies encouraging other people to build business off of their APIs.
The path for hackers to hack on APIs is clear. Hack away for the fun of it. But, I don't fall into that camp. Nor do most business minded people. So, where does that leave us?
Enter the 5th horse: the search underdog, Amazon.com, with its obvious search ambitions is changing the game....
Now, all we need is a competitor or two with the same model and equivalent products, so that we can keep their pricing honest. Then, we can really feel secure building a commercial venture off of other company's APIs.
Then, the hack day type events that Yahoo is having can be transported out into the real world of enterpreneurs and non-yahoo employed hackers. You don't need to be a yahoo (pun not necessarily intended) to build useful commercially viable mashup services off of APIs.
Which would be nice. Cause the rest of us would like to play too!
Sidenote: Now all Alexa has to do is support the AttentionTrust with all of that Attention data they have locked up in their vaults, and the field will really be levelled. There is certainly more value that can be derived from that data - beyond a simple zeitgeist - for advertisers, consumers, publishers and "platform players" alike.