So, for anyone who still doesn't understand how twitter can be useful here is a good explanation of its impact on the G20 protests. Think of it as a universal, burst broadcast medium. It becomes useful when everyone writing about a particular event or topic colludes to use a common tag, in this case #G20, so that everyone interested can filter just that topic and hear the chatter of what's going on. Search and filters (which is just really watching the changing results of agiven search) is an essential part of it.
BBC NEWS | Twitter on the front line.