When uploading a file to UCM there will be a little percentage indicator (eg: 0%, 10%, 50%, 80%, 100%, complete!)
This will help while uploading large files. This is a HTML5 + Flash upload progress feature.
Please report any issues with this new feature on the forum.
You can swap back to the old uploader by going to Settings > Advanced and changing file_upload_old from 0 to 1