I usually say I'm polyamorous, because most polyamorous people know the term, but otherwise yeah. I also live in Portland, and hang out with crowds where this is more common than normal. I did end up dating one monogamous girl, but she was completely okay with it - work occupied 90% of her life, and having a partner that didn't mind seeing her once or twice a month worked out very nicely for her.
I generally bring this up well before asking someone out, so that I can get a good feel for their reaction (often first or second meeting - just talking about my life makes it pretty clear I date multiple people. "Oh, today I hung out with girlfriend A and watched Farscape, then got a haircut with girlfriend B")
I also tend to emphasize my particular style of polyamory, which centers on honesty and the idea "It's not cheating if everyone involved has agreed to play by different rules". I've found signalling "I'm poly, NOT someone cheating on their spouse" is important :)
Have I ever mentioned how envious I am of people who live in Portland...
Information that surprises you is interesting as it exposes where you have been miscalibrated, and allows you to correct for that.
I suspect the users of LessWrong have fairly similar beliefs, so it is probable that information that has surprised you would surprise others here, so it would be useful for them if you shared them.
Example: In a discussion with a friend recently I realised I had massively miscalibrated on the percentage of the UK population who shared my beliefs on certain subjects, in general the population was far more conservative than I had expected.
In retrospect I was assuming my own personal experience was more representative than it was, even when attempting to correct for that.