First, a central bank can, in theory, print money as fast as they can. However, this does not happen in reality because issuing too much currency will feed inflation only and eventually destroy the economy.
Unlike a central bank, Bitcoin miners are not interested in maintaining the stability of the Bitcoin economy. While a central bank would choose to control the amount of cash floating in the market (admittedly, they are not doing a good job either), Bitcoin miners will want to make the best value out of mining and will dump the mined coins on the market whenever they can make a profit (the arbitrarily set limit of 21 million is nothing scientific and does not accommodate the real Bitcoin economy activities in any way).
Here comes the sharp difference, that in my opinion, would likely bring Bitcoins down.
Second, looking back, the initial miners created their fortune too fast, with too little investment. The result is that those people will dump the coins they have anytime the market is good. This would likely be a disruptive force that crashes the exchange rate. Unlike people having to pay a fair amount of money to get Bitcoins (whether through using expensive mining machines or buying the coins direct on market) this year, those pilot indeed can dump the coins and make a profit at anytime. This means that the market will always face the risk that some unknown adopter just arbitrarily dump the coins and then crash the market. Think of April 11, a tender of sale for 20,000 coins eventually pushed the market downward, until today.
Unless someone can resolve the issues, I would say, be cautious.
I think Bitcoin will survive for many decades but could potentially take a backseat to some of the newer alts. By modeling coin generation after the rules of physical gold, the upcoming Goldcoin (GLD) fork will address many of these stated limitations.
The successful currency must have; 1. massive consumer adoption, 2. practical methods of exchange (android), 3. adequate but finite supply, and 4. enduring miner incentive.
I also think the winning alt will be viewed as both a currency and a commodity.