Amazon's Alexa unit, which tries (poorly, some might argue) to track web traffic, has been embroiled in a spat with the site Statsaholic, which until recently was called Alexaholic.See also reports on this from Dare Obasanjo and TechCrunch.
Statsaholic's strategy was to take Alexa's data and present it in a matter that's far more usable than the way Alexa presents it.
Amazon seemed to tolerate, or even encourage, Alexaholic, until it built all of Alexaholic's functionality into its own site, at which point it went on the attack. First it went after the company's domain name, Alexaholic.com, which was arguably infringing on Alexa's trademark. Then Amazon blocked off access to its graphs and data, effectively disabling the renamed Statsaholic.
See also my Nov 2005 post, "Is Web 2.0 nothing more than mashups?", where I said:
Companies offer web services to get free ideas, exploit free R&D, and discover promising talent. That's why the APIs are crippled with restrictions like no more than N hits a day, no commercial use, and no uptime or quality guarantees.
They offer the APIs so people can build clever toys, the best of which the company will grab -- thank you very much -- and develop further on their own.