Have I got a photo to sell you

Actually, I'm blegging for information. Has anyone used online photo printing services like ZenFolio, SmugMug, or Shutterfly, either as a photographer selling images or as a customer? Maybe your wedding photographer used a third-party site?

As a corollary, do you or does anyone you know buy stock photos for publication?

No, I'm not quitting my job; but with a backlog of 30,000 photos—some of them already sold as stock, some of them more than once—the wheels in my brain have started to turn. (Maybe it's the MBA.)