So I'll start off with my answer to a question that pops up pretty often, and is asked by both veterans and new polypeople, to wit: "What's the difference between an open relationship, and a poly one?"
One way of looking at it is that 'poly' can describe the mindset and 'open relationship' can describes the factual arrangement, like "lovers" and "married".
If you make a big Venn Diagram (remember those from high school logic classes, with the interlocking rings like a partial Olympic logo?) where the two circles are polyamory and open relationships, they're pretty close to overlapping, but there are parts of each that exclude the other, and I'd be willing to bet that the "open relationship" part is slightly larger. For example, people can be single, yet honestly describe themselves as polyamorous; others can be in an open, non-monogogamous relationship, but not be honest with their partner/s about what they're doing and with whom, hence not polyamorous. There's bound to be a good amount of disagreement with me on this, but I firmly believe one of the principal hallmarks of poly involves open and honest communication - and while poly offers a ton of leeway in defining the terms of your relationship, it generally doesn't extend to situations where information is hidden, or one or more partners cheat (by acting outside the predetermined rules, whatever they might be).
In addition, many people have "hookup buddies" with whom they have no emotional connection beyond that required for casual sex from time to time. There's debate over whether or not that qualifies as polyamory, which by its literary definition seems to require some degree of "amory", or emotional bond - but I'll say those relationships count as poly, as long as everyone involved knows and consents.
I tend to fall into the camp that says people who have sex outside a loving relationship aren't poly. For some people, sex and love are very different things (one of my ex's comes to mind...but that's another story). Just like if you're in a kink relationship for play, you might not consider yourself poly because that's play, not love.
I feel that a lot of people prefer the term "open relationship" to describe their own version of what is in fact polyamory. Facebook, for example, uses it as a relationship option, so that tells me it's more mainstream. I think it has a positive connotation (i.e. open and honest) and maybe the word "polyamory" squicks out some people because of associations with "polygamy".
I like your thought that poly is the mindset and open relationship is the product that results. You might be a monogamous person who happens to be in an open relationship (I was, for a while until I came out as poly). And at the same time, you might be a poly person who is in a mono relationship because you've agreed to follow those rules. The difference will probably be that poly people reserve the right to renegotiate those rules at some point in the future, whereas mono people tend to understand those rules to be set in stone.
So can we say that "love" is to "sex" what "poly" is to "open relationship"? That works, unless you're one of those freaky-deaky people who has sex just for fun :P