Looking back, a lot of my OTPs were bordering on OT3s, depending on circumstance. Frex, if I were in Trek fandom now, I'd be one of the kids writing nu!TNG 'verse, Picard/Beverly Crusher/Jack Crusher all the damn time. The first M/M story I ever wrote was actually M/M/F, and that was for yet another children's cartoon. I don't have any F/F/F OT3s, but now that you've brought it up, I'm already going over permutations in my head with my various F/F 'ships. :D

In TW, I've got my favorite triads (guess) and my "Meh, I'll read it if the porn is good" threesomes. Threesome porn is kind of like pizza: even when it's not exactly the toppings you wanted *ahem*, it's pizza. *shrug*