Thanks for all the feedback on this - this is definitely one of those features that would be great to see in the product, but requires careful thought before putting it in due to the security risk.
Is there a reason that IE in full screen mode won't fulfill your requirements? If the application must be cross-browser, why doesn't a maximized borwser work for you?
Also, what keys would you want enabled, and why?
Feel free to reply privately via the forums if you'd like.