You're now given a rank based on your score. Gain points for collecting Tire Valve Caps, crossing the Finish Line in a good time, etc, Maintain them by not getting hit or.. uhm.. becoming flat. Using powerups can help you through levels, but foregoing them gives you bonuses to your score.
An "S Rank" Golden Hubcap replaces the one you'd previously received by clearing the level within a certain time. ... but clearing the level within that time is a great way to rack up points.
Progress toward your rank and toward your hubcap are both reported as you play in the upper-left corner of the UI.
The post-level stats screen also gives you more details, such as your time, number of times you got popped, number of.. uhm.. "skulls", and so on.
I'm still working on calibrating the scoring system, so we might see changes from time to time.