One thing is certain -- "trending topics" is a misnomer. "Newly popular" is more like it. Twitter's algorithm grossly overweights the 'novelty' of a topic (over-weighting the change of frequency that a topic is mentioned). Topics popular for an extended time are affected.
In some instances, such as a breaking news event, natural disaster, an RIP, a coach getting fired...trending topics works perfectly. Such topics often jump from a low to extremely high rate of mentions. This also causes problems, specifically hashtags..."#noonelikesyoubecause" is the third trending topic currently, joining a long list of hashtag trends which dilute the usefulness of trends.
The trending topic algorithm fails in one big area -- topics which remain highly popular for weeks or months. It's happened with other topics, such as the Oil Spill and Justin Beiber. Now it's happened with Wikileaks. From everything we've seen, it's simply a bad algorithm. #imwikileaks, for example, is currently the top trending topic on Twitter, when you set your location to Germany. In our view, Twitter does its users a great disservice by labeling "newly popular topics" as "trending topics". If a topic is popular for an extended period, it should trend. That includes Wikileaks, and even Justin Bieber.