Streetview photographs are taken from a much higher viewpoint than a person walking along the street. So, someone erecting a 6' fence to afford them some privacy would now need something in the region of 8'.
In essence the goal posts have been moved and, with it, the comfort zone. Anyone walking down my street has some business to physically be there whereas now, what can be defined as "their reason" is somewhat different. You buy something on eBay and the seller can, for example, take a look at your house. Quite why they'd want to do this is beyond me but then I would not profess to being able to explain what the next person chooses to do.
I think it's hard to pin down exactly what might be intrusive, it simply a case that your post code now leaves you more public than ever before (potential number of eyes and what is visible).