Sneaky little tip... it IS possible to avoid a blue shell, as long as you have a mushroom or get to a boost pad at precisely the right moment.
Notice how the shell spins about your head, then stops for a split second before smashing you in the face? Do you see where I'm going with this?
In that split second between the shell stopping its spinning, and descending upon you with its Norris-esque ass kicking abilities, use a mushroom, and you will out run the explosion.
It's incredibly tricky, but possible.
WARNING: successful completion of this technique may impair your vision due to the incessant tears of joy that will invariably fill your eyes.