Yahoo has removed the commercial restrictions on Yahoo Updates API, its social streams service that provides real-time user activity data. In addition, Yahoo increased the usage limits to make the platform more viable for commercial websites.
Yahoo's announcement explains the changes:
Until today, Yahoo!'s social data and user activity streams accessed via the Yahoo! Updates API or Updates Firehose API have only been available to developers on a non-commercial basis. With this announcement, developers can use social data for commercial purposes as long as usage complies with all terms and conditions.
The Updates API includes Flickr uploads and movie ratings, among other user actions on Yahoo. The new limits allow 100,000 calls per day for applications, or 10,000 per hour per IP address.
It's common for free APIs, especially from larger companies, to come with commercial restrictions, though many often ignore money-making mashups. When Bing API was released without usage quotas, there was a lot of discussion (see comments) about whether its non-commercial terms made the quota-less discussion moot.
Yahoo seems to be going about this openly, allowing for commercial use while maintaining a small amount of control over just how much access developers can have. We list Four social Yahoo APIs in our directory, including Updates and Yahoo Contacts.