As a percentage of GDP, the debt will double in ten years, given current projections.
what this will mean over time is, the money we spend every year to service the debt, i.e., pay the interest, will go up and up. This will have two effects: 1) we have less money to spend on roads, the military, police, etc. 2) it crowds out private credit, meaning that there is less money that can be loaned to businesses, to consumers to buy houses, etc., because the government is competing for the money that people and businesses are ready to loan. This will drive up the interest rates, which means we will have to pay even more to service the same amount of debt. Some people on Yahoo! Answers think we can just increase the debt forever, but 'taint so.
After servicing the debt, the percent left over for other government services will necessarily shrink rapidly.
Think about it: the $20 trillion debt we will have in 10 years, at 5% interest, say, equals $1 trillion a year in interest, which is $3000 a year, roughly, for every man, woman, and child that we will have a that time. And that's just the interest, not any of the other costs of government.