Well the results from the "nissan" test are in, I tagged 2 of my existing photos with "nissan", here are the photos....
As you can see not a nissan in sight (other than in the tag).
Overnight the view count on my whole photostream jumped up (no comments or favourites though), seems as though every single photo in my stream was viewed 4 or 5 times. This has never happended before.
My theory is there is a "bot"/"spider" that is watching for the "nissan" tag in flickr photos and then scrapes through the whole photo stream. Why it does it multiple times I don't know...