I personally couldn't be in one because I can't even imagine how I'd be fine with my boyfriend sleeping with other guys.. But I've also experience guys who have been in open relationships and if it works for them, then heyho alls good in my eyes
But saying that, I don't view 'open' relationships as relationships really, if you love someone and want to be with them, then you wouldn't want to sleep with other people.. I find them to be cop outs really.