The Poly Vignettes: Sharing Success & Happiness thread (posted above) is delightful and contains lots of happy stuff.
For me, loving and being in relationships with two wonderful people at once has been amazing. I've grown so much as a person in the last few years, much of it as a direct result of that. I'm better at communicating, more responsible for my own feelings/actions, and more patient and kind, I think.
Plus, I have so much love and support...I feel very lucky.