I've sold enough to pay for the site and I plan to keep adding images as long as I live!
Two things that occur to me, big prints sell better - 40" wide is my max, and thats the size I do most of, although the other better selling size is around 20x16. The other thing is a web site is a brilliant way to refer people to your work - not long ago I used to prefer visits for folks to look at prints (and hopefully buy!) but this meant keeping a large stock of prints, and inevitably someone wanted a print in a size I hadnt got. So now if someone wants to look at a lot of what I do I refer them to the web site, and more often than not this works as a starting point.
Advertising the site is something ealse though. I've got a small permanent display of framed stuff in a nearby high class eating joint, and I make sure the web site details are almost as visible as the prints. This seems to work pretty well, and on the whole things (web site sales wise) are getting better - although I'm no where near making a proper living from it. I just think its a good way of showing work, and a good way for people to have a good look at what we as photographers do all around the world.