“I agree with most posters here, the couple involved are flaming nitwits, however how much do we have to opt out of?”

Whatever’s reasonable. It’s reasonable to be required to opt out of Street View, as the useful service it provides would be impossible to provide if it were an opt-in service. Everything else should be taken as it comes, but the examples you give are utterly ridiculous.

“If our WiFi traffic is accidentally harvested,”

It already is. If you don’t encrypt your traffic, anyone within receiving distance can run a packet sniffer and look at the contents. If your next-door neighbour runs such a program while diagnosing his own network and accidentally captures your network traffic (while it’s travelling throgh his property, else he’s physically trespassing anyway), then he’s had access to your network data.

It’s down to you to “opt-out” by either encrypting your traffic or placing your router in a place where nobody outside your property can access it.

“if audio recordings accidentally include what we say in our house”

It depends on what the circumstances are. There would have to be a very good reason for this to be captured for it not to fall foul of anti-bugging laws, and I can’t think of any situation where capturing audio (a completely transient quality) would be useful in the same way as capturing physical geography.

“if someone accidentally videos all the mail as the mailman puts it in our mailbox”

Again, what possible purpose could there be for capturing such information. Maybe a video version of Street View, but it’s unlikely that such a thing would violate your privacy, and it would also be covered by the same arguments made about Street View now – if it’s happening in public, it ain’t private. Your mailbox is in public view of the street, therefore unless the information given is far greater than a passer-by would see, it’s not a privacy violation.

“If google had cameras pointed at hospitals around the country to count the number of pregnant women entering and children exiting, would that be acceptable? What if they did the same thing at a drug treatment clinic? Should pregnant mothers be responsible for discovering that their images are on the internet and be required to opt-out of every website that creates or posts the content?”

What utterly ridiculous arguments. Hospitals are privately run buildings. To provide such images, Google would need permission from the hospital and would need to provide a damn good reason for wanting to make such images public. In any case, your issue would be with the hospital who allowed such images to be made public, not with the service provider (Google). Any hospital would be able to opt-out, and they would need to have authorised Google’s cameras in the first place (what you’re talking about is a permanent installation, not a literal drive-by as with Street View). In any case, cameras are already installed in hospitals, it’s just that they haven’t decided to make such images public.