Does the celibacy rule cover masturbation? Good question. I never bothered to think of it, since the Catholic Church considers masturbation to be immoral (read: "against the rules") for everyone. Wikipedia has quite an article on clerical celibacy - noting that there is a chance of inaccuracy in Wikipedia entries, I have to say this article looks good.

But anyhow, masturbation is one of those things that isn't talked about - kind of a "don't ask, don't tell" situation. It warrants a paragraph (2352) in the Catechism of the Catholic Church, where it is referred to as "an intrinsically and gravely disordered action." A priest I trust says it's the sin he hears most often in confession. He didn't say more, but I got the impression he wished people could find more important sins to confess.

But in answer to your question, priests and nuns are supposed to be exemplary in the practice of the virtue of chastity, and refraining from masturbation and other "impure" things falls under that category, rather than under the category of celibacy.

What do I think of it? Well, I don't think of masturbation as sinful, but it's not something I'd go around recommending as a beneficial spiritual practice - but it's something people do as a normal course of nature, and I see no reason to condemn it.

-Joe-