Been there, done that, had a long-term polyamorous arrangement going with two girls about 10 years ago. Neither girl was "ideal girlfriend material" by herself, but each made up for the other's flaws. One was far more intelligent, a better conversationalist, and shared more interests with me outside the bedroom. The other was loyal, submissive, passionate, and had a very strong physical chemistry with me along with a combination of being bi-curious and having one hell of a voyeur fetish, but we really worked primarily as sexual partners and not much else.
I'd do it again if I got another perfect combination like that, but I prefer to do my shopping "one-stop", you dig? Future multiple-partner sexual encounters will probably be more of the casual variety.