One of the worst experiences is browsing for a file, and waiting for it to be uploaded. I wanted to avoid that at all cost. Ultimately, as a writer, I just want to drag an image onto the text and have everything else handled behind the scenes.
Did the same thing here at Jekyllhub. Drag and Drop for file uploading is too nice an experience to ignore. I put in a javascript spinner over the text to let the user know their file is being uploaded, but it shouldn’t get in the way of writing. I also have a regular file field as a fallback in case javascript is disabled or something.