So I've been playing around with the bars and beats info from the track analysis file and in general, I've found their accuracy to be pretty inconsistent.
I know that there is huge complexity to the algorithms for finding beats, bars, etc. and I definitely don't expect it to be 100% perfect. But based on other EchoNest apps I've seen – particularly Tristan's Swinger – it seems like it should be possible to very accurately identify the placement of beats and bars in a track.
In one experiment I've done (which you can play with here: http://www.jordansthings.com/blog/?p=16), I play a sine beep at the exact time the EchoNest track analysis file tells me a beat falls. Sometimes it's pretty on, many times it falls on the upbeat, and other times the tempo seems correct but the beep falls nowhere near the actual beat. I'm also seeing the similar issues with the bars information.
I was hoping someone at EchoNest could speak to the accuracy of the beats and bars data and possibly confirm that the level of inconsistency I'm seeing is expected. Did Tristan do any massaging of the beats / bars info for The Swinger app?