photokeywords is an experimental tool which allows you to gather keyword info from a microstock site. I have to say I'm not to sure I condone the harvesting of keywords like this, it's better than just cutting and pasting the keywords from another photo.. but not much!
The concept is simple, you enter a say three keywords and the site searches the database at shutterstock for some images. You select the images that are most like yours and then photokeywords displays all the keywords within those images as a list. It orders the listing by the most popularly searched keywords. You can then select and reject which of the keywords are relevant to your photo and finally a list of the keywords is displayed for you to cut and paste.