The scoring algorithm is pretty complicated and SongPop does not plan on releasing that. In general the faster you guess vs. an opponent, the higher the score. If you guess songs in a row, there is a bonus. If you miss a song, all the previous bonus doesn't get applied to the next one you get right - you really have to be faster than your opponent to catch up and/or hope they miss a song. We display the guess time in 1.x seconds, but we use milliseconds, so what you see in display (because of space issues) is not necessarily what we are using for scoring. That's how you can play three rounds and be 1 point different from someone. If there is a tie, then the user who started the challenge gets the win.
We hope this explanation was helpful. Please email us at firstname.lastname@example.org if you have any further questions.