I'm actually quite fascinated with this little tool from Google...  apparently its quite controversial and I can see why.

So far I've not really done a lot with it, other that leave complaints on websites to warn other people about dodgy dealings...  one of the main comments that sticks in my mind is a site where I bought my girlfriend some flowers and she did not get anywhere near the amount of flowers that were in the picture, I complained directly and got little worthy response, so decided to take action. I think people are usually more driven to complain using Sidewiki than they are to give due praise.  That’s just human nature I guess.