> Even the US dollar and euro, supposedly bastions of stability, have seen their exchange rate jump from US$0.80 per euro in 2002 to US$1.60 in 2008 (100% jump), only to drop back down to US$1.20 in 2010 (25% drop), then jump to US$1.45 in 2011 (20% jump), only to drop back down to around US$1.29 today.
If we needed to buy everything in the US but store all of our wealth in Euros, this would be the right comparison. But since we don't, "stability" means low and predictable inflation for the Euro and the dollar. The exchange rate matters for Bitcoin because wages, goods, and services are all denominated in non-Bitcoin currency. Look at inflation over the same period and you'll see that the dollar really is a "bastion of stability" (in that narrow sense, the Euro is too... but the Euro's got other problems beyond the scope of this discussion that make me reluctant to vigorously defend its stability).
If we needed to buy everything in the US but store all of our wealth in Euros, this would be the right comparison. But since we don't, "stability" means low and predictable inflation for the Euro and the dollar. The exchange rate matters for Bitcoin because wages, goods, and services are all denominated in non-Bitcoin currency. Look at inflation over the same period and you'll see that the dollar really is a "bastion of stability" (in that narrow sense, the Euro is too... but the Euro's got other problems beyond the scope of this discussion that make me reluctant to vigorously defend its stability).