I actually like the idea of a National Warning System - we have a warning system in New Jersey and it can be very useful especially when telling you about missing children, or storms coming.
To my question though: The current system relies on you watching TV or listening to radio - what about all the people who are working and are only connected to the internet- how are they going to be warned. A National Warning system will only work if it reaches the entire population (or at least the vast majority).
If there is a real emergency broadcast we'll probably find that the telephone systems, cell phone (voice and text) and email systems will be chocka-block full of messages - and this is likely to cause more problems!!!
When the stage collapsed at the Indiana State Fair some weeks ago, a lot of people in the crowd couldn't get through to their families on their cell phones, because everyone present was using them at the same time. Some people (including someone I know who had been sitting right in the spot where the stage hit) were able to contact their families to let them know they were okay - through Facebook.