There are already competing digital currencies. For one, Litecoin is based on the Bitcoin algorithm.
If you have been paying attention, Ron Paul has been pushing competing currencies for some time and for good reason.
I plan to buy some Bitcoin, some Litecoin and whatever else comes along that promotes freedom.
Bitcoin has some shortcomings and an ideal currency wouldn't be so speculative. Everyone should confront the same barrier to entry for a good medium of trade. Individuals shouldn't be punished for coming in late in the game. At least for a fair and honest medium of trade.
Early adopters are making a killing in BTC at the moment. This is exactly why competing currencies are a good thing as they work to level the playing field.
A free market will correct itself. Competition is good.