As John says, this certainly opens up entirely new classes of search engines and other applications that can be built by leveraging this data.
Alexa is charging for its data, but it isn’t much.
The first 10,000 requests per month are free. Thereafter, requests are charged at a rate of $.00015 each (just 15 cents per thousand requests.). For example, if you make 100,000 requests to the Alexa Web Information Service during a given month, you will be charged $13.50. Your first 10,000 requests are free, while your remaining 90,000 requests are charged at a rate of $.00015 each: .00015 * 90000 = $13.50.
We’ve been working with Alexa data at BuzzLogic (which is what Persuadio has morphed into) and it is an easy to use API that is adding tremendous value to our analysis at a low cost. This is a gold mine for developers and I agree with Battelle and Nick Carr that this is a signal event as it is an easy way to flesh out background information about sites. As I was saying in the post below, the future is going to be on the record and this is one of the ways we’re going to find out more about who’s doing the talking.