It's a bit of a moot point, as evidenced by the replies above. The only vulnerable target would be merchants that run their own node. As the network matures there would be less of those, and more outsourcing the service to an IPN provider, not unlike PayPal works. The IPN providers can setup shop in a jurisdiction that does not recognize the patents.
Bitcoin is built on standard cripto primitives: Hashes, hashcash, Merkle trees, p2p networks. The idea of using hash-cash to achieve Byzantine fault tolerance is to my knowledge an original one. Any patent for Hashcash itself is either close to expiration or has prior art . Ditto for Merkle trees (patent expired in 2002
). The only problem is ECC which has patent issues
for some implementation techniques. ECDSA as used in Bitcoin (Libeay/SSL) should be free.
 C. Dwork and M. Naor, "Pricing via Processing or Combatting Junk Mail", Lecture Notes in Computer Science 740 (Proceedings of CRYPTO'92), 1993, pp.