I'm not sure I would call audiosurf a 'racing' game but alas that seems to be what it is classified as. Regardless of whether or not you think of it as one, it WOULD make sense to add features from racing game, specifically the one where it tells you if you're ahead (+) or behind (-) of your previous run.
In normal racing games this would be done by time. There are specific parts in the track where the game would record the time (say, 1:23). There may be 4 or 5 of these per lap. Then on your next lap it will record the time again in the same spots and COMPARE them to the previous ones. So say you got 1:23 on the first lap for the first point, and then on that same point (but second lap) you have a 1:28 then you went -X% (don't feel like doing the math at the moment :p) but had you done 1:18 on the second lap, then you went +X%.
Of course with audiosurf you don't have laps. So instead, it would be nice if the game would compare the numbers on each separate run.
It would be nice to have at the very least 3 'comparisons' per track. Maybe have it like from 0% complete to 25% (and then it spits out the first number, which for audiosurf instead of time would probably be # of points) then from 26% to 50% it gives you your 2nd one, and then from 51%-75% it gives you the third one and you might as well at a fourth from 76%-100%.
Doesn't anyone else think this would be an awesome addition to the game? That way you can compare how good you're doing in certain parts compared to the best time you played.