I always see these "peg to something else" responses and it makes me wonder why no one bothers to ask the obvious question:
If "X" must be pegged to "Y" for "X" to be stable, then what is "Y" pegged to that makes it magically stable?
If enough people (merchants and users) were transacting in "X" then why would they need or care about "Y"?
That is the thing, for example a coin that is pegged to the US dollar is stable in the sense that it will always have a value of one dollar but the dollar itself is not stable it has lost its purchasing power during the last century at an alarming rate and that rate is accelerating due to the US government printing more and more dollars, that is why I think bitcoin go it right you must create a coin with limited supply and let the people to decide how much each bitcoin is worth.