The National Debt - Is It Okay?

Currently the National Debt is hovering at 8 trillion 6 hundred billion and change. So what's the deal? Is it out of control? Should we pay it back?
During most of my studies of Economics I have always taken the stance that a national debt, while it isn't necessarily a good thing, was okay. As long as the GDP continues to grow exponentially did it really matter if we were in debt? Initially I believed no. Now, though, my thoughts have changed dramatically. Why do you ask? Our debt is no longer our own.
zfacts.com/p/461.html Check out the current debt climb.
More and more of our debt is now owned by foreign nations unlike the past. We must pay that money back now.