I can't tell you how many times I've accidentally hit the Save and Upload button when I was meaning to hit the Paste button.
I really wish I could cancel the action when the Upload box appears. It can't be the active window while the IPTC box is up, so you have to close the IPTC box, then close the preview, then tab over to the Upload box. By the time I've done this, the picture may have already uploaded, so then I need to fire up an FTP program to try and kill it. Arghhh. (this just happened to me again)