Interesting topic. A computer nerd friend went over all this with me a year ago. My immediate and lasting concern was just what achillies pointed out - the government and banks will stop at nothing to shut bitcoins down as they catch on.
Ultimately the banks/gov will likely attempt to make bitcoins illegal. If that happens I'm guessing it is going to be damn hard to transfer your bitcoins into dollars. Even the individual face to face sellers could get shut down by stings just like drug dealers. Selling bitcoins through an exchange could also be setting you up for tracing of dollar transferrs into your bank account from the accounts used by known buyers. Not many buyers/sellers are going to risk jail time for a moderate commission.
The first real battle here, imo, will be the almost certain legislative attempt (or arbitrary "policy change" by the executive branch - since nobody gives a damn about Constitutional procedure anymore) to make bitcoins illegal. The second battle would be the court case challenging the legislation/policy.
Given the fact that Congress and the Presidents continually give away hundreds of billions of dollars to the "too big to fail" banking elite, I'm guessing there's not much hope on that front. Given the history with Egold, Liberty Mint, etc it appears that the courts will also fail to protect free market currencies like bitcoin.
Then I'm guessing there will be one last strategy. Bitcoins could be sold anonymously through the torr exchanges and actual cash or gold be shipped in return - much like they are used to purchase drugs now. This would be a little harder to track/prove than direct transfer to a bank account (as can be seen by the fact that the gov is apparently unable to currently stop these torr exchange drug sales). Not a perfect solution but probably worthwhile for many people in a high inflation/tax environment.
Then again I am not a computer expert so it is hard to understand some aspects of bitcoins & exchanges. All in all it is a fascinating system to watch and speculate about its evolution. At the very least it is one more worthwhile attempt to fight the banking monopoly.