Patent Reform Act Proposes Sweeping Changes
I would actually argue that first-to-file has very strong "theory" justifications, in addition to being far simpler to administer. Consider two people who invent the same invention. The first "invents" first, but keeps it a secret. She is slow to work out all of the details (to "reduce to practice" in patent parlance), to turn it into a commercial product (or else she would run into section 102 statutory bars against later filing her patent), or of course, to file the patent. Perhaps she has problems with finding the time or the necessary funding; perhaps she is simply lazy. (Of course, she can't be too lazy. The law requires that she be "diligent" in reducing to practice and in filing a patent, or else she loses out to the later inventor who is diligent and files first.)
the useful solution that is easy to justify (if you believe in patent theory)
The second inventor invents the same thing two month later. She did actually invent it entirely independantly of the first inventor, or else she can't get the patent under either first-to-invent or first-to-file. The first inventor, remember, has kept the details of the invention secret. Inventor two works hard to reduce to practice and promptly files a patent. She also quickly brings the product to market, all while inventor one is dawdling.
Who deserves the patent? I would say inventor two. Of what use are inventor one's efforts to anyone? Sure she "invented" the thing first, but why would I want to reward people who invent quickly, but then just sit on their inventions? Of course, you can come up with other stories that might shift the argument one way or the other. The point is that there is a value to having people make their inventions public quickly (so that others become aware of the idea, so that others know that a particular problem no longer needs to be solved, and so that others become aware that a patent is likely to cover a particular area in the future), and filing a patent does this, as patent applications generally are published 18 months after filing. (The patent reform proposals would increase the number of applications that must be published after 18 months, by the way.)
This isn't about making it easier to process new patents quicker. Relatively few patent applications become involved in "interferences," two or more inventors attempting to patent the same invention. Where this change would make the biggest change is in the courts, where inventors claiming the same invention fight it out or where patent defendants try to invalidate a patent based upon a later filing that was arguably invented first. These court cases are pretty messy. First, the question of when an "invention" is made is often not clear cut. Years can pass between when you first get the idea to try something and when you know it works and have worked out the messy details. When during this period does "invention" occur? Second, these questions often are very difficult to prove, since much of the relevant work goes on largely within the mind of the inventor.
it's easier and will allow the patent office to process new patents quicker
Perhaps the bigger reason for the change, however, has to do with international harmonization. Every country on the planet other than the U.S. has switched to first-to-file. If further harmonization of patent laws is to occur, the U.S. is clearly going to have to switch as well. What the U.S. hopes to get as quid pro quo, however, is a switch by Europe to allow a "grace period" between when you publish details about your invention and when you must file the patent. Current European law says that if you make your invention public before you file, you lose the right to file the patent. The U.S. lets you file up to a year after you make your invention public. Japan gives you six months and is otherwise a bit more restrictive than the U.S. The lack of a grace period in Europe means that inventors interested in the worldwide market effectively have no grace period; making your invention public in the U.S. prevents you from later obtaining a patent in Europe. I think a world-wide uniform 12-month grace period would be a significant improvement in the system, one that would well serve the open exchange of knowledge that the patent system is suppose to promote as an alternative to trade secret protection.