All Twitter APIs will soon use HTTP error code 400 for calls beyond your rate limit. One of Twitter's most popular services, the Search API, currently uses error code 503. You'll want to update any of your applications that use Twitter search so that they're looking for the right code.
Gliffy, a browser-based diagramming and flowchart tool, today announced the public availability of their new API (technical details at our Gliffy API Profile). The four year old company announced the new API on its blog, noting that Gliffy hopes to take advantage of the growing trend of companies that are unlocking their APIs to extend the reach of their applications and data.