Currency - whats its all about?

I'd have to disagree with Gunny a tad bit on the Depression. The Federal Reserve manipulating rates to a very low point, which encourages borrowing and investing, created a bubble in the 20's that could not sustain itself. Fractional reserve banking also allowed the banks to lend our most of the deposits to such investors. When the bubble inevitably collapsed, banks went under because their loans were defaulted and they could not honor the deposits. This entire collapse left a few VERY rich and most of the country very poor. Economic growth ground to a halt and Roosevelt's interventions and cartel schemes prolonged the Depression. It wasn't until the country had a reason in WWII to actually produce which then led to years of prosperity afterwards.