Every once in a while I will jump the gun and drag a whole whack of photos onto the upload screen ... only to realize moments later that these are the HUGE (2800+ pixels) versions and I meant to upload smaller versions. But now I have to wait until all of these are uploaded before I can delete them all. And since they are the huge versions, it takes forever!
It would be great if there were a Cancel Upload button somewhere on that page, that could bail me out of my stupidity. The only other option I have found is to exit the browser, then restart it and log in again. A decent enough workaround, but far more time consuming than a simple cancel button.