Same problem here.
I only do footage, so I use FTP.
Nine times out of ten the interface get stuck and I have to reload the whole batch. If and when I finally manage to upload and go to the keywording part, nine time out of ten the page get stuck again and I have to close the page. After that there is no way that I can find the page allowing me to manage files.
The whole uploading process looks like a bad joke.
I had already given up after a first trial many months ago, decided to give it another go, but I am seriously thinking that I am wasting my time.
Actually going back I realised that I have a few clips in my portfolio from my first trial and I even have made a few sales (not sure how many because numbers don't seem to match). I didn't even think I had some files successfully uploaded!