IANAL, but I believe that prior art can still kill a patent. The patented stuff is still supposed to be the inventor's original work. (The patent office may not be terribly diligent about searching for prior art, and establishing prior art can still be a massively expensive pain in the ass... but that's another rant.)
What first-to-file certainly did change is what happens when two claimants try to file a patent on something that wasn't prior art. It used to be that the patent office looked through the inventors' records to try to establish who was the first to invent the non-public technology; now, it's just the one who was first with the patent office paperwork.
First-to-file != prior art. It just means if there is a dispute between two parties A and B, A invented the technique first but B filed it first, the law now states that B owns the patent.
This does not mean that I can now go and claim that using electricity to create logical meaning thus creating a computing machine is patentable (even if nobody patented it before)
