I used to get annoyed by people hotlinking to my images. Recently I've noticed a correlation between hot linked images and results from image searches. For example a couple of weeks ago VW bus images were hotlinked from a couple of forums, and suddenly my biggest search phrase was VW bus.

I've started not to mind image linking quite so much. Visitors from image searches often stay to have a look around. I really should watermark more photos with the domain name though....