The Boston bombings provide a clear example of what I wrote about earlier when I said that legislative band-aids like firearms bans don't prevent mass killings. Someone who is determined enough will find a way to harm people. These two men didn't need guns to carry out their attack, though they used them later trying to escape. I doubt that registration and background checks would have prevented them from obtaining those guns either.
If anyone was actually interested in logical consistency, Americans would now start pushing for a ban on pressure cookers. After all, the only people who really need one are those who live at altitude. Maybe we should run background checks and require certification of residency at an altitude greater than 2,500 feet for pressure cooker purchases.
How about attempting to regulate black powder? Even if you track fireworks and model rocketry purchases (among other readily available sources of potentially explosive materials) you wouldn't be able to stop someone armed with fairly low-level knowledge and skill from making their own. Historical reenactment enthusiasts have even made black powder by hand, using historical techniques and raw materials like livestock urine, potash, wood charcoal, and sulfur. It's considerably easier to get the necessary ingredients now, in a modern industrial society, than it was when black powder was a military-grade material. There's even been some talk of taggants in commercial preparations, though that wouldn't matter until after the fact, when trying to track down where the materials for the bomb came from, and wouldn't help at all with homemade preparations.
Instead of focusing on the specific tools used in an attack, attention should always be directed toward intelligence gathering. This is the information age; information is paramount. Anyone with a knowledge of basic chemistry can make several different explosive materials in their garage easier than someone can cook up a batch of meth, and look how many tweekers seem to be able to manage that.
Granted, this particular kind of attack is one of the most difficult to detect. Lone nutjobs or small partnerships with no larger group affiliation or outside funding are brutally hard to find before they do something irrevocable.
Law enforcement maintains a tradition of secrecy regarding terrorism that is usually counterproductive. Help from the public has time and time again proven crucial for finding those responsible for attacks like these, before they can commit another attack. There should be more transparency and better information sharing from government agencies. Citizen training programs could also help in getting good-quality, timely information for investigating before and after attacks; providing more wheat and less chaff in citizen reports.
Panicking doesn't help. Legislation drafted while panicking certainly doesn't help. The most effective parts of the PATRIOT Act, for example, have been in interdepartmental information sharing, not the draconian provisions circumventing the Bill of Rights that allow actions like warrantless wiretaps, secret searches of property and the installation of spyware and keylogging software, or indefinite imprisonment without trial.
How do Americans win against terrorism?
By sharing information as openly as possible. The identification of the Boston bombers was made by the public, not through the gathering of secret surveillance or the use of high-tech facial recognition software.
By defying terrorists and not letting them manipulate us into the responses they desire. Every erosion of rights and freedoms makes our society less democratic and more authoritarian.
By not being scared. Fear was the motivating factor behind two major wars, huge changes for the worse in the American law and justice system, and hysterical counter-reactions of such ignorance that Sikhs worry that they're going to be the target of hate crimes when an attack by "possible Muslims" occurs.
Bans of X and Wars on Y do not work. They do not make us safer. They do not make us more free. They do not even allow us to more quickly apprehend the offenders after an attack. They do not improve our lives in any way.