The Web Cryptography Working Group of the W3C has produced further documents describing Crypto APIs and when they might be useful.
First we have a revision of the working draft of the Web Cryptography API which was initially published in September 2012.
We also now have a first draft of Web Cryptography API Use Cases, effectively filling in a missing section of the two previous drafts. The use case scenarios included cover the use of the two APIs, with each describing a potential web application using these APIs. There are scenarios with code snippets for banking transactions; distributing video services to web-enabled TVs and Set Top boxes, encrypted communications via Webmail, storing documents in the cloud, and one that explores threat models in the context of local storage. A scenario for "off the record" real time messaging needs additional details.
All three documents have the status working documents that are under discussion.