How to Set Limit on Friends Request / Day

Has anyone written a mod or know of a soultion for setting a limit on how many friend requests can be made per day by either a certian user or user type.

Facebook does this and we are having problems with some people friend requesting every new member on our site when they don't know them. It is a turn off for professional social networks so we need to have a way to set limits.

Thanks for any help