If there was a concerted effort to "shut it down", where are the vulnerabilities?
The potential for the Bitcoin client to communicate with other Bitcoin nodes has been discussed at length, but what about the other parts of the Bitcoin ecosystem that have we become dependent upon? If they disappear (e.g., denial of service, or taken down), will Bitcoin continue to function as a currency and payment system?
What are the most important systems that we are dependent on and how are we affected as a result if services from these systems end?
For an example of one such service -- what would be the effect if BlockExplorer.com were to be forced offline.