... and it is not only the fitness which is important, after all you do not want to hurt yourself (or someone else) while doing a race. You eally should be confident about riding closely packed in the middle of a group, and you should have some practice cornering fast (especially if you want to do a criterium). Cornering fast actually can be great fun (once you got the experience that is and dont freak out or hit the brakes...). Once in a rce with relatively open corners the girl riding next to me told me that it was her first race and that she did not really no how to corner and could I please be slow and keep my distance ... it kind of freaked me out and I tried to move far away quickly.
But having said all this, the racing part is fun. More fun though if you come technically prepared.