It really doesn't dominate after a while. We went for a 50" (against the OH's judgement) and it very quickly 'blended in'. In fact, I was soon wishing I'd gone for a larger one! As for 3D......haven't bothered with it as I don't feel it's really up to scratch yet.
Go for the largest (as long as it's of good quality) screen you can. Even if it seems huge in the room at first, it very quickly appears to be smaller than it actually is, so doesn't dominate the room.