"We’ve built a very simple application on our labs website where you can listen to music and help us <i>improve the state of the art</i> in tempo estimation."<p>No. We are giving you data that you use to improve <i>your</i> tempo estimation algorithm. If you wanted to improve the state of the art, you would <i>share</i> the data you collect.<p>In particular, you note the MIREX competition (<a href="http://www.music-ir.org/mirex" rel="nofollow">http://www.music-ir.org/mirex</a>) earlier in your post. Share your data with the MIREX competition, and make it open for use by others, if you want to improve the state of the art.
I sampled enough of the songs to get about 500 points(20-30 minutes) and they really need to increase the variety of samples. Most of the stuff was older pop hits (50's pop), some country, 1 rock song (Disturbed - Ten thousand fists), and a couple of old rap songs.<p>I'm used to listening to metal, industrial, hardstyle, house, etc. All my answers are going to be biased towards slow because even though the song may be at 120bpm it still feels slow to someone who normally listens to things closer to the 150-200bpm range.<p>A better sample to test will produce better results.
Even with the app it seems really hard to find the beat. It's really easy to find the bass hit though, so I wouldn't be surprised if a lot of the tempos are off by 1/2 or 1/4.