The Ad hominem area is intended for use when a member (or a non-member) feels the need to attack someone, as opposed to attacking their arguments.
This could be as simple and direct as flat out abuse, or as subtle as a detailed geneological analysis of a specific individuals motives and predjudices. When the knives come out, and there seems no alternative to telling someone what you think of them, (and why), this is the place to settle things.
On the validity of Ad hominem assaults, Wikipedia has this to say: "Premises discrediting the person can exist in valid arguments, when the person being criticized is the sole source for a piece of evidence used in one of his arguments."
Knock yourselves out.