It's rather impressive that you can actually view your videos, photos, PDF files and Word, Excel and PowerPoint documents right from your Box.net account on your iPhone. You can also play music files that are stored on your account, so it's like expanding your 8 GB or 16 GB iPhone. I was able to play several tunes this way without any noticeable performance issues and this was strictly over 3G with no WiFi enabled.
Everything is in real-time so that means the app can monitor activity with your box.net account. Whenever someone has added a file or document to a shared folder on your account, you'll be able to see it instantly.
There are a slew of useless apps for the iPhone, but this is not one of them. Being able to store files from your mobile device to your online storage account is incredibly useful for business and pleasure. The ability to share files with iPhone users without needing to rely on email attachments (which can get blocked, delayed or lost) is another big benefit, especially for mobile users.