I only own a Wii. I don't really need anything else right now, since I haven't even beaten all the games I have.
The 360 interests me mildly, and I might get one, but only after I know that the hardware problems have been fixed and the console costs about 199. For the Elite. Maybe that'll never happen.
The PS3 has that whole "wait til the good games come out" mystique going for it. Team Ico's new project, a new Jak and Daxter, (definitely bored of Final Fantasy by now), possibly Ratchet...and I'm stalling. I honestly can't think of any other games that I'm excited about. Again, I'm also waiting for the price to come down to under $200.
That's when I usually buy a console, under $200. I only bought a Wii at $249 because it was the Wii. I was too damned excited for that system because of what it was.
So it looks like I will be a Wii owner only for at least the next year, maybe into 2009. I waited last generation, too. I had a PS2 first, then got a Cube when Metroid Prime 2: Echoes came out. I don't think it's unusual for Console owners to be exclusive for the first couple years in a generation.