What matters is the ability of the government in question to pay.  The US enjoys the benefit of having never defaulted, so its credit rating remains strong.  Currently, our interest payments make up somewhere between seven and 10% of the federal budget.  The problem is that this percentge is rising fairly quickly.  As long as we can continue paying the interest, we'll be able to borrow.

It is a problem, though, in the sense that governments should try to maintain low debt levels, so that they can spend if they need to.  Why put down your weapon if the enemy won't put down his?

We've run deficits in all but four years over the last half-century -- '69, '98, '99, and '00 being the surplus years.  (Check me on 1969, though.  It was somewhere around that time.)  But, up until Reagan, the deficits were falling as a percentage of GDP.  That's not wholly Reagan's fault.  The Democrats -- remember, this is the latter portion of the era of Democratic dominance in Congress -- in Congress at the time were not exactly fiscal saints, themselves.  And both had to deal with the Fed purging inflation and sending the economy into the worst recession since the '30s (based on unemployment).

Conservatives want live babies so they can raise them to be dead soldiers. - George Carlin