I don't think the current low levels of the US dollar are sustainable. You have to remember that interest rates in the US have been cut to rock bottom, while they remain higher in other countries.
For instance, right now I could borrow money from a bank in the US at about 5% and invest it at over 8% in Australia (and those are just the interest rates that I, the consumer, can get -- I could do even better if I were a hedge fund or something). This is a huge arbitrage opportunity, and I'd be crazy not to take advantage of it... unless of course the US dollar goes back up over the course of my loan and wipes out my profit. The fact that the apparent opportunity exists means that the market is obviously priced on the assumption that the US dollar is going to go back up eventually, and is currently being held down only by the low interest rates.
Take my example. I currently live in Switzerland and am now moving to California, for entrepreneurial reasons.
But I must say it has become less attractive if you look at the Swiss Franc to US Dollar: http://finance.google.com/finance?q=usdchf
In 5 years the Dollar has lost 25% ! That means that now Americans in average are 25% poorer compared to Switzerland than they were 5 years ago.
And the worst that can happen to America is if the smart, driven and hard working people it has been attracting for centuries stop coming. They are the ones that drive America's growth. And with the dollar down the tubes they might think twice before following their American Dream.