Many sites offer some statistics like The hottest topics in the last 24h. For example, Topix.com shows this in its section News Trends. There, you can see the topics which have the fastest growing number of mentions.
I want to compute such a buzz for a topic, too. How could I do this? The algorithm should weight the topics which are always hot less. The topics which normally (almost) noone mentions should be the hottest ones.