I've heard that you know you're bilingual when you start dreaming in your second language. I'm not sure if that's true, but I have had dreams since I've moved here where I've spoken in Spanish with less then more accuracy.
I remember being suspicious when I first moved here that I wasn't exactly speaking real Spanish in the dreams. Just Spanish-like talk.
But the other night I discussed flooring and how I wanted something arranged in a random pattern with a builder of some kind in my dream. And I don't know that I know all of the words needed to intelligently have that full conversation, but I woke up in the middle of the night and knew I'd been discussing it in Spanish with him.
And I was very happy. :)