I've only done the 'fuck a stranger' thing a couple of times and, fun though it was, it does leave you feeling a little empty. Finding someone you click with is hard enough without having to go through it each time.
The important thing is to be honest with each other from the outset of what it is you want from the relationship (I do consider an fb to be a relationship - just not the traditional kind), if you both have the same idea then it will work, if you're looking for different things then it wont - I suppose the same can be said of any relationship.
H.x