I was hijacked and added to a nutter's circles
I tried it at first, just to see what was going on. I didn't post anything, just read streams (or whatever they are called). About 50% of posts on a stream were adverts for some product.
Later, there was an 'awesome picture' stream which did indeed have lots of very impressive photos, probably lifted from somewhere else. One was so good, and so beautiful (to my eyes), that I commented on it, adding to the many comments already posted.
Two days later, on logging in, I noticed that I had been added to one of the circles of some guy who was Italian, a minor EU functionary and worked in some EU offices in Brussels (I read his profile). This was a man who had 50,000 people in his circles and a big cheesy smile photo of him at his office desk - obviously a sad nutter.
I managed to ban/block him, eventually; but I bet I'm still listed in his circles.
So, when this sad nutter goes on the rampage with a machine gun, after poisoning the local water supply, the anti-terrorist police will have my name as one of his 'associates'. Great!