Deafness in cats is correlated with having a white coat. This doesn't mean that every white cat is deaf or that every deaf cat is white but if a cat is white, it is more likely to be deaf.
If a white cat has blue eyes then it is even more likely to be deaf. Again this does not mean that a cat with orange eyes cannot be deaf as well or that a white cat with blue eyes is necessarily going to be deaf, all it means is that there's a higher likelihood of a white cat with blue eyes being deaf.
Because of this is, it is generally a good idea not to have two white cats breed. When two white cats breed the likelihood of deafness in their kittens increases by a large margin.
For more cat care info read
Cat Care Fundamentals.

We also recommend
Complete Cat Training.
Here's a short video I made of her.
http://www.youtube.com/watch?v=e7RfwuAuOr4
She loves to play and hardly ever gets scared (she can't hear anything so loud noises don't scare her off).
I feel kind of silly mentioning this, but if I ever have to get another kitty (can't live without one) I'd want it to be deaf. I've never seen a more affectionate, loving and playful cat as my Meeka.