Twitter played an important role during the mumbai terrorist attacks. The community that formed around the #mumbai tag, actively discussed how they felt and provided live, uptodate information filtered from different news sources. This was a tipping point for twitter that transforms it from a social tool to a news source. The most important factor here was that the dynamic community that emerged around the #mumbai tag was not constrained to discuss one single topic. Something that News sources struggled with as the developments happened so quickly in this critical event. Most news sources need to stay on a story for at least a few minutes before they can move on to another story.
As #mumbai became popular, trolls showed up on twitter and posted messages with the hashtag only to draw attention to their website or link to other sources of little or no relevance whatsoever to the current crisis. This made me wonder, what if anything could be done in Microblogging environments to restrict users from misusing hashtags. A quick glance over at the current use of #mumbai shows a number of such sources that should probably moderated. I am refraining from naming any particular users but this is something that could be better dealt with by the community as a whole.
One suggestion I have is to create a new hashtag like #ban followed by the user name and the hashtag for which the user should be banned. Once a particular user is #ban tagged by several people from the community -- Twitter can automatically ban the user from further posting on the specific topic. This would be a simple and effective means for a community driven moderation in twitter.