U.S. patent law, at its simplest level is a bargain between the U.S. Government and inventors. The bargain essentially being "you tell everyone else how you did it and we'll give you a limited monopoly to exclude others from doing the same." While Thomas Jefferson and others weren't thrilled with the system...it is the system our founding fathers established.
Blawger and patent attorney N. Stephan Kinsella recently penned a very interesting critique of our patent system in an article entitled "There's No Such Things As a Free Patent." Stephan's article questions whether the costs of the patent system outweigh the gains it provides and mentions some potential alternative systems others have proposed (reward systems, nationalized IP, taxes to fund R&D, copyright-like patent terms, etc.). An interesting read...
UPDATE: For those of you reading via RSS, the comments for this post continue the discussion...