I am so glad this thread was resurrected - wow, I started it over 2-1/2 years ago. I have wanted to revive it myself a few times, because I always wondered why more independent solo poly people didn't weigh in on the topic. I don't think PMM has their forums online anymore, but this topic went on for pages and pages over there.
For me, personally, I set my own boundaries but do not make rules. My main one is pretty much the same as Marcus's - no one has a say about my relationships but me and the person I'm involved with, and that applies to metamours as well as as to other lovers of mine.
I've more to say but no time right now, so I'll check the thread later.