I've been hanging around a bunch of poly people in the recent years, and I would say most are V-shaped. Or W or something. I'd say everyone is friends, and date around but once a relationship becomes more serious they usually like to meet with the new partners. And sometimes do become good friends. What I find tough with polyamory is the constant negotiating of boundaries and expectations. In a traditional relation, of course that's important too. But you already have a base framework that you can adapt to, and the situation is not shifting as constantly with the coming and going of new interests. Poly is like playing the relationships game on hard mode. My friend when on a date with a poly person recently, and was just overwhelmed by the amount of disclaimers and current relationship structure explaining that was necessary before even starting anything. It's like the communication part becomes a full time job. Maybe it's just my personal bias, but the almost therapy-like language poly people use to discuss their relations would put me in a perpetual state of eye-rolling if it was my life. I'm super happy for all my friends that seem to be doing poly right and loving it, but from the outside it seems like more trouble than it's worth.