Box.net's UX activity progress design pattern is what makes box stand out from the crowd. They 'get it' and truly understand how to design a user experience many other websites should mimic.
The specific elements that inform the user of what's going on: 1. background page faded – focus on activity 2. 'Uploading 6 files' – user knows what's happening and how many files are being uploaded 3. Visual progress bar – shows relative progress that's dynamic 4. Upload metadata: upload speed, total file size, upload rate and time left to upload 5. Up-sell for quicker upload speeds 6. 'Hide Popup' – further options available to user while files are being uploaded