After a few days of going ballistic, I've finally mastered the Ninja.
Like the guides above, wait til you complete the game so you can unlock the races for goal attack.
The races that tend to gave me the biggest headaches were the unordered races. So i tackled them first, then the longest races next.
The easiest way to do all the goal attacks, is to use the Ninja motorbike, and to become very familiar with the weight transfer button. It helps if you have a general idea of the city layout.....
To turn even sharper, or to avoid a costly slide / crash, as you turn, let go of the accelerator, tap handbrake and weight transfer simultaneously into the direction you want to go, then reapply accelerator. If you're still sliding, hit a nitro.
Using this method, I was very confident in my ability to win every time - not counting the damned pedestrians. In fact I just downloaded south central an hour ago, and have only 6 more races to do :)