Interesting piece on mediabistro.com about what buyers want (and don't want) when searching for stock photography. They gleaned these tips from PhotoShelter's School of Stock. Here's a nice snippet from the story:
"Survey respondents indicated the worst categories in stock photography, in terms of quality and breadth of available imagery, were healthcare (88%), multicultural and diversity lifestyle (86%), senior citizens lifestyle (86%), and consumer technology and products (84%). And don't even get them started on the dearth of photos of multi-ethnic senior citizens in hospital settings playing video games."