While an individual user may use Twitter primarily as a conversational tool or a broadcast medium, in its totality, Twitter operates a lot like a wiki: as a knowledge-sharing, co-creation platform that produces content and allows its consumption. Conversation is perhaps the most simple and obvious form of collaboration, but would anyone claim that Wikipedia is a conversational platform? Despite the presence of information sharing, co-creation of an end product, and even discussion pages, Wikipedians on the whole aren't having conversations. According to this argument, Twitter is no more a conversational platform than Wikipedia is.
del.izzy is a free service that lets you search through your del.icio.us bookmarks. Wait a second, doesn't del.icio.us already let me do that? What's different about del.izzy? del.icio.us is a great service, but when you search through your bookmarks, you are only searching through tags, titles and descriptions, not the page content. del.izzy lets you search through all content, including title, description and page content, for all your bookmarks.