2) Take a look at Japan: http://www.tradingeconomics.com/japan/government-debt-to-gdp

220% of GDP and no one is worrying. Why? It's bond yield is so low: http://www.tradingeconomics.com/japan/government-bond-yield (unlike Greece: http://www.tradingeconomics.com/greece/government-bond-yield)

The US incidentally has a bond yield roughly double Japan http://www.tradingeconomics.com/united-states/government-bon... Even though it has a much lower debt to GDP, it is paying almost the same interest per GDP!

And that's the funny thing about solvency. As long as investors give you low interest rates, all is well. If they decide you will be insolvent, bond rates rise, resulting in a self-fulfilling prophesy where you actually become insolvent.

Solvency is of course inversely correlated to debt to GDP ratio, but there are tons of other actions at work.