Hashrabbit is a twitter popularity racetrack. Each race takes place with respect to a hashtag (or twitter 'track' keywords). Hashrabbit dutifully reads all the related tweets and tallies who is mentioned the most. @hashrabbit can even tweet at you throughout the duration of your race to let you know who is winning.
Why? Create a race with a conference hashtag to see who are the biggest hoppers and shakers at the conference. Use hashrabbit to conduct a poll or vote via twitter.