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.
Yes, definitely. That's part of what I was getting at with my reply elsewhere in this thread (http://news.ycombinator.com/item?id=2540866 ). The perceived beat can actually be different depending on who is listening, and what they're focusing on.