I think it's a good idea to put the P word front and center, before even the first date. I don't think I'd go on a first date, anyway, if the person didn't already know that about me.
I met the new guy I'm dating on OKC (where I really just had a profile up so I could snoop around other people's profiles, out of curiosity, and maybe make new friends). My profile mentioned polyamory, and a pretty full dance card (and bisexuality, which is a turn-off for some lesbians), because I didn't want to start making friends with someone if either of those things are deal breakers for them.
It's good to have the information out there.