http://www.usdebtclock.org

down at the bottom, it has the Liability Per Taxpayer item. is that the amount of taxes that i'm supposed to pay to cover my portion of the US Unfunded Liabilities? think i might need a payment plan.

I think that's assuming no corporate taxes or other sources of revenue (ie simply total debt/tax payers).
So yes, it would be assuming the US government didnt' levy duties, collect fines, or tax commercial endeavors.

The US debt as a % of GDP is on the high end relative to the rest of the developed world (I think it's the highest).

It's high, but nowhere near the highest.

Japan, Italy and Greece all have worse debt ratios, as do several developing countries

The chart at the site below cites the IMF as of 2010. There might be more updated numbers, but I'm sure Japan, Italy and Greece haven't moved past us.

Italy and Greece are at 115% and Japan is at an astounding 194%.

According to the chart, the U.S. is at 84%. For context, here are some of the other countries that are more financially sound (in comparison to the previously mentioned three):

France: 78%
Canada: 70%
Germany: 74%
China: 19%

Looking at the chart, it's certainly hard to say having 84% is terribly bad, even though I'm not against some cost-cutting measures, but many of the countries in the 0-20% range don't really have terribly strong economies.

Of course, now I've probably changed the trajectory of this conversation. :)

In fairness, I've found two different charts/sites (one of them wikipedia with 2011 estimates) and while the exact percentages are different on all of them, they do seem to place each of these countries in about the same place ranking wise.