Last year Ron Paul introduced the Free Competition in Currency Act of 2007 which would make alternate currencies legal, though not change other aspects of what you can do with currencies (e.g. money laundering would still be illegal).
Few young people realize that until the 1964-1968 time period it was possible to bring your dollars to the government and get precious metal on demand. This gave the dollar real worth. Since that time, the government has found that it can simply make more money out of thin air and spend it on government programs to generate votes. As with any supply and demand equation, when they start running the printing presses to make more dollars, the dollars you have in you bank account become worth less. You're losing money value and the government is gaining money value, but your 'taxes' are low. One can see this in inflation charts which start to skyrocket in the 1970's, relative to decades previous. Interesting note: if we measured inflation today the way we used to back then, our inflation rate would be 11%.
The Wall Street Journal recently ran a graph showing the value of the dollar vs. gold vs. oil. If we look at the start of the decade until now, if we were holding euros instead of dollars, gas would only be about $2.70 at the pump - that extra $1.30 can be viewed as lost power of the dollar. But, the euro is no panacea either - if you compare the price of gas to the price of gold, it's nearly flat. How about $1.20 gas? I actually saw $5 diesel in CT last weekend.
Not surprisingly, the government decided to stop keeping track of 'M3', or the money supply of the dollar recently. Private economists have continued the calculations and it's easy to see why the government doesn't want to talk about it.
So, back to the beginning, the government has taken irresponsible action with the way it manages the value of its currency, and they have laws preventing people from opting out of their mismanagement. Afraid of a little competition, are they? Experience shows that the most likely effect of competing currencies, even ones that mimic the way the government operated in your parents' generation, would be to pressure the government to exercise some restraint. Of course, if this competition is illegal, they'll continue with their outrageous devaluation.
Folks who think a little competition helps to keep markets fair, and monopolies hurt them, would do well to contact their representatives in government about the aforementioned bill.
Thus spake the master programmer: "When a program is being tested, it is too late to make design changes." -- Geoffrey James, "The Tao of Programming"