I think we may over-use the term "community", and I am probably as guilty of this as the next person.
A community is a group of people that shares a set of values.
In human communities, intent, belief, resources, preferences, needs, risks, and a number of other conditions may be present and common, affecting the identity of the participants and their degree of cohesiveness.
The word is often used to refer to a group that is organized around common values and social cohesion within a shared geographical location, generally in social units larger than a household.
(Both are from Wikipedia)
I would like to propose that calling any online of the online poly social networking systems a "community" may be giving it more weight than it deserves and may increase expectations beyond what could be considered reasonable.
I believe that a community needs to share a set of values whereas the poly "community" shares precisely one (and most often they can't even agree on what that one really means). Therefore to expect that just because a group of people are poly that they will/should have other things in common or should necessarily all get along is unrealistic and it puts unrealistic pressure on those communities.
I have met some highly obnoxious people who self-identify as poly, and some very nice ones too.
I like mixing with poly folk simply because I like the idea of not having to hide the fact that I have two loving relationships, but that's about where it ends as far as expectations. The rest is up to the individuals involved. As Ceoli says, I like to explore the power of "and".