We've seen an architectural pattern emerge over the last two years that deals with the expanding variety of computing devices and the exploding number of APIs used in modern applications. This pattern is API Virtualization - applying a virtual layer above the API itself to deal with the different concerns that come into play when delivering an API to different device and machine endpoints as well as across a range of different classes of business relationships.
One of the big shifts that has occurred in application development is the move from libraries to APIs for use of pre-written code. APIs enable access to not just logic but data and the the computational power required to render that data appropriately. The Facebook and Twitter APIs are good examples of this, but there are many more including Paypal's X.com, Ebay, Amazon, Netflix, Sears, Blockbuster, Best Buy, MTV and Google.
While applications like Siri which use 20 or more web APIs are still unusual, most applications use several APIs to deal with access to content, social networks, events, identification, payment, and other concerns. These APIs change frequently, as do the applications that consume them, resulting in a web of dependencies and causing chaos in the development lifecycle.
API Virtualization enables these different concerns and dependencies to be isolated from the application or API provider, resulting in a cleaner development process and higher-performing applications.