I'm using CarrierWave / Fog in a Rails application to upload videos to Amazon S3.
Is there a way to determine the progress of the upload, so that I can display the upload progress being made?
CarrierWave and Fog don't have that kind of functionality natively; you'll need a front-end uploader to display progress stuff. When I had to solve this problem I used jQuery file upload because I already had jQuery in my stack. There's even a post on CarrierWave integration so you can just follow the instructions there to get a progress bar working for your app.