The Leahy-Smith America Invents Act (AIA), H.R. 1249, was passed by the U.S. House of Representatives on June 23, 2011, and by the U.S. Senate on September 8, 2011. The bill now goes to President Obama to be signed into law. http://www.uspto.gov/patents/init_events/aia_implementation.jsp
One of the most important provisions of this Act is that it introduces a "first-to-file" system as opposed to the "first-to-invent" system that is currently in place. This will bring the US system into line with the "first-to-file" system used in Australia. While it has its detractors, I welcome this change because, to some extent, it saves my clients having to adopt a different set of rules for the US. In the complex world of patent practice, any such alignment is to be welcomed.
Here's the wiki on the difference between the two systems: http://en.wikipedia.org/wiki/First_to_file_and_first_to_invent