I've been using Black's for the past little while to get my digital pictures developped. For the most part I'm pretty happy with the prints. I usually end up paying somewhere around $0.30 for a 4x6" print, and the quality seems good. The only time I had a problem with the prints I returned them and they reprinted at no cost.
However, getting my pictures to Black's is a bit of a pain. Their only interface right now is an HTML form that allows you to upload 12 images at a time. So when I have a few dozen pictures I have to upload them in batches...and keep track of which ones have been uploaded, and which ones haven't. That means clicking on the "Browse" button for each image, and selecting the image from the list of all images in a directory. If I happen to miss one, I'm basically screwed, since they don't keep track of the original order of uploaded files, and am left to look through each of the images on my computer one by one to check if it's been uploaded.
This probably isn't specific to Black's, so don't think that I'm picking on them. It's probably a consequence of the relative immaturity of the online photo processing industry.
What about some kind of online photo service API? It could be XMLRPC / SOAP or some custom protocol, it doesn't matter much to me. The simplest case of this would just have to support user authentication and image uploads. Then we could write real client-side programs that would integrate much better with our photo management tools. Imagine being able to click "print" on an image in your photo management software, and having an order queued at your friendly neighbourhood online photo processing centre! You could manage the rest of the transaction via your browser if necesssary, like handling delivery and payment options.
Has anybody heard of anything like this?