I do understand the squeamishness about the opt-out system, but I think, on balance, it's the right thing - that is, subject to the caveat that the awareness campaign is sufficient to give everybody the opportunity to opt out if they want to.
I've never felt particularly attached to my body (I know that sounds a bit mad, but I've always felt that 'me' and 'my body' are two distinct things - 'I' am in my consciousness, and 'my body' is just a weird fleshy vehicle) - so I'd be happy for it to be used for anything useful. As a being, I have taken resources from the earth and from society, and I feel a very strong obligation that they need to be given back when they aren't useful to me any more. Honestly, I'd be fine to be fertiliser if my organs aren't any use for transplant.
I'd feel much more protective over my husband's body, I think, but I know he feels similarly to me, so his decision is already made.