When I first linked my Flickr I was amazed at how many matches came up, I think it was over 200! Alot of these would be people using blogs or just collections of images they liked, often directly linking to the flickr page. In this instance these are harmless and as there is no commercial gain you cannot chase for payment. However, I did find some of my older images of my travels when I was younger (

However, Im pleased to say that a recent case has been resolved and I have received payment (via Paypal). It was for an image of my travels in Jordan that was being used on a German travel company website. Whilst not enough to buy a new DSLR its a welcome sum and shows that their business model works.
I would encourage other members to join (its free) and see if their beloved images are being mis-used "out" there.