Recently TurnItIn has released an iPad app, allowing grading and commenting of student submissions. Despite the limits functionality of this in terms of the complete service, I am finding it much more efficient to comment on student work using the iPad app rather than the web interface. And anything that increases my effectiveness gets my vote.
One big bonus of the app is that you can sync a class assignment. This means marking offline. The web interface relies on an always on Internet connection to work. Now I can sync an assignment, mark offline and then resync when back in a networked area.
If your school / institution uses TurnItIn and you have access to an iPad, then I encourage you to download the app. I am sure you will find it useful.