As evidenced by activity on the del.icio.us blog, steam is picking up on feature development for the social bookmark service. Now you can make queries againt your bookmarks and receive the results in JavaScript code or JSON, language neutral JavaScript objects. This will make it easier to incorporate del.icio.us into AJAX, browser side JavaScript, applications since the apps won't have to internalize XML.
Also, this potentially provides a standard client side object model for tagged bookmarks across all JavaScript del.icio.us applications. And conceivably any other bookmark service (Furl, spurl, unalog) could output data in the same format, leading to an "industry" standard.