The current recession is now definitely going to be worse than the Great Depression. The excesses that created the mess are being stretched beyond sustainability. Now even Niall Ferguson and Nouriel Roubini agree on this.
The main reason is US government, taking heart from USD's global reserve currency status, is priming the economy at an unimaginable scale. Taking the US example lot of countries are attempting a similar strategy. It would be important to note that this is not simply printing money but creating debt.
The current strength of USD is due to global slowdown. The world will soon realise that depending on US consumption is not going to happen anytime in near to medium term. As the relative strength of domestic markets start, we can forsee a battle for share of pockets of savers. This, to my mind, will be the begining of the end of US dollar.