An interesting piece of research I found on my travels through the internet, with a handy graph as well.
It is some market research by The Nielsen Company, asking people in New Zealand searching for properties online what they wanted to see. Top of the list is Large Selection of Images, third is High Quality Images and sixth is Large Images. The conclusion of the research is that "Image related resources are highly attractive for real estate website research". Granted the survey was only taken in one country and the sample size was 1206, but it does show that people who are looking for somewhere new to live want to be able to see professional images of the prospective properties. As I've mentioned before, most images on estate agents websites are poor, but with a little time and investment they can be greatly improved.