The America Invents Act, signed into law in September 2011, has brought the most sweeping changes to the U.S. patent laws and your rights under those laws in 60 years. A critical change that goes into effect on March 16, 2013 is the transition from a “First Person to Invent” system to a“First Inventor to File” system.
This change rewards inventors who are the first to file their patent applications, as opposed to inventors that are the first to invent. The “First Inventor to File” system also includes an expanded universe of prior art that may be used to bar a patent application. This expanded universe of prior art is designed to encourage inventors to be the “First to File” their patent applications.
As a result of these upcoming changes, it will be preferable in many cases to file your patent applications prior to March 16, 2013. This includes new provisional and non-provisional patent applications (even if they can claim priority to a previously filed provisional or non-provisional).
More information regarding the America Invents Act can be found here.