No, that's really not important. The way the site-owner interface works, I will imediately notice if sumbissions are comming in while I am uploading as there will be a very bright red icon on the blue interface, and then I can just skip a few pages ahead with only two or three double uploads at the most, that's not a problem.
If two of you are uploading the same images at the same time, that's another thing, because you wouldn't notice them piling up in my inbox before they are published.
However, there seems to be a problem that the uploader on the site does not allow you to switch to "upload from URL" mode, so you would have to first save the files on your hard drive and then upload them from there. Which easily tripples the amount of work it takes to get an image up.
If anyone has an idea why that is and what can be done about it, please tell me. Or maybe there's a problem with my browser only and it worlks for other people, I don't know.