It's like an API festival here at Gluecon. I tweeted that this afternoon. But it's not just Gluecon, though - they're one of the hottest topics in discussions about cloud computing.

In his presentation today at Gluecon, John Musser of Programmable Web illustrated how hot APIs have become and how they've matured.

Perhaps most illustrative is his "API Billionaire's Club."

Members of the club include Google and Facebook with 5 billion AP calls per day. Twitter has 3 billion per day. Ebay has 8 billion per month. NPR gets 1.1 billion calls per month for its API-delivered stories. Saleforce.com gets 50% of its traffic through its API.

According to Musser, it took eight years to get to 1,000 API's but just 18 months to get to 2,000. This year, the number of API's are double what they were last year on a month-per-month basis.

Internet/platform as a service (PaaS) API's are now number one. That's illustrative of the increased usage of services like Amazon S3 and all its competitors. Maps are the number three API, dropping from the number one spot last year. Social API's are number two.

REST API's are far surpassing SOAP.

There's a real energy here at Gluecon around the discussions about APIs. The room was packed for the presentations on the topic.

We'll pour more into the topic in later posts.