The new rules are now official and a first to file system has now been implemented by United States Patent and Trademark Office.
This first-to-file is pretty much governed under the 35 USC 102(a) and the exceptions under 35 USC (b). Simply speaking 102(a)(1) – has to do with publications and 102(a)(2) – talks about the filing date.
Here’s a chart (PDF) regarding the statutory framework for the first to inventor to file new rules.
Also effective filing dates are now the earliest filed patent anywhere in the world (for foreign applications, we used to have the US effective filing date and foreign priority date, and would apply prior art differently depending if it was 102 a/b or e)– this a bonus for companies that file in other countries first, as they now get the earliest date for all prior art purposes.