If I were to leave my house unlocked, I'd not expect people to enter without permission, even though they probably could do so. But if I were having a conversation, perhaps a meeting using a microphone so that everyone could hear, and I left my windows open so that passersby could hear every word, well, I'd have to expect that and be OK with it. No?
Google is in all sorts of trouble over Wi-Fi sniffing by its Street View cars. And lawyers now argue that the data was not collected accidentally as previously claimed, but that the cars were deliberately programmed to collect the data.
And many are comparing this to the unlocked house example, so evil and sinister, big bad Google silently creeping into your private property to steal from you. The thing is, that analogy is flat out inaccurate. My microphone broadcasting info up and down the street is a far more technically accurate analogy. And yes, if you yell outdoors, clearly and free for all to hear, well, then you can't complain if sometime writes it all down.