As stated previously in this thread: it's already in effect here as "presumed consent" and the family can intervene, unless you have opted in.
But , seeing as this seems to be getting rather heated, I'd like to considder the following:
The opt-out system has the benefit that you can have a list of people who are so attached to their organs that they don't want them replaced when they're faulty either.
Should save a few organs to save people who didn't opt out.
That's not the legislation over here right now, but reading some of the comments in this thread, I'm starting to considder this.