#8 - Misuse of our Private Messaging system will result in consequences. You are not to spam members using the PM system. You are not to send invitations to other sites using our PM system. You are not to harass others using our PM system.
Somewhat of a gray area. Spamming and harrasment are pretty arbitrary for each individual in this context. I would say that if you ask someone to stop PM'ing you once...they better stop or deal with the consequences. Further, ladies if you are doing this, better make sure the guy is welcoming of these types of solicitations. If you are asked to stop sending them, I highly recommend you do exactly that.