Microsoft's latest version of its search API (our Live Search API Profile), which was released last November as a public beta, seems to be gaining quite a bit of momentum. According to a recent post on the Live Search Blog, the API is serving more than 3 billion queries per month, more than 5,000 applications to use the API, and queries from third party sites account for 80% of the API's query volume.
This past Valentine's Day, DuckDuckGo announced via Twitter that their search engine had "received over 1,000,000 direct searches yesterday for the first time ever!" A major accomplishment for a search engine that is essentially unknown. And this search engine has an API.