What if ISP's block port 8332? Hypothetically, if it were a well coordinated NSA-type shut down and ALL ISP's suddenly blocked port 8332 (major ones anyway), how would the Bitcoin system immediately handle it?
Bitcoin can be configured to handle any port for both peer-to-peer communication, as well as JSON RPCs. However, as Bitcoin clients do not encrypt their messages, it would still be fairly easy to filter out Bitcoin-related activities. One could then switch to using Bitcoin through TOR, or the developers could implement message encryption if needed be.