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.
In the short time that I have used it, Twitter has grown quickly to play a major part in the way that I interact with fellow colleagues and professionals from around the world.
How do you decide whether a technological development is significant or not? Here's a simple rule: if the mainstream media — as represented by, say, Daily Mail columnists — are baffled by, or contemptuous of, it then it's probably worth paying attention to.