Internally, I don't think any of the horror stories would happen. Decisions would have to be made, fast, about what spending to cut. Federal employees would probable get vouchers for awhile until things get sorted out. Lots of furloughs, but air traffic controllers and prison guards would most certainly stay employed.
By the way, this Planet Money on debt was interesting:
http://www.npr.org/blogs/money/2011/07/20/138518262/the-tues... (TL;DL the US is near 100% debt to GDP, countries historically run into problems when they exceed 90%, but it's not a guaranteed outcome, and Britain reached debt to GDP rations over 250% after the war, yet still exists)