[ronp]

Currently US patents give priority to the first to invent. So, if you invented a widget and spent six months perfecting that when your next door neighbor filed a patent one day after he "invented" it, your ability to prove you were first to invent (through evidence like your research notebooks, etc.), the USPTO could refuse or invalidate your neighbor's patent and award you the patent. That goes away with first to file, which means that the people with the deepest pockets who can afford to file patent applications quickly will wind up winning the race. Most of the rest of the world uses first-to-file.