Twitter's algorithm for determining Trending topics, used by TwitGrids, has been updated to focus on topics which are "most breaking" and "immediately popular". Twitter's term is 'emergent'. This new algorithm dramatically improves the quality of trending topics. As we all know, the value of trending topics has decreased dramatically over the past three months.
One issue we notice: long running news stories might suffer (i.e. the latest oil spill) in the short term until Twitter tweaks the algorithm.
TwitGrids spam filters all tweets within each trending topic. Spammers often tweet using trending topics; we filter the spam out to maintain a good user experience for our users.