I must say, online PU through facebook, msn etc just doesn't seem cool to me.
I think it should be done in moderation, arranging dates, displaying high value, social proof, pre selection with FB pics etc
But to keep a convo going through msn chat with a HB you don't really know. I wouldn't attempt it unless for what I said above. To easy to come across wrongly, make mistakes, appear childish etc lol
No harm in it obv, just to easy to create the whole lets just be friends kinda SPAM
Hope that helped.