This person apparently didn't use anything.
Unreliable media, combined with what I have seen a doctor or two give statements on about things removed from patients suggests nails and/or ball bearings were used.
A high volume of similar items removed from patients not present in the environment in quantity suggests they were part of the bomb.
IF these improvised devices used such components, this actually illustrates the impotence of these components compared to say, the high explosives used in suicide vests and car bombs in Israel.
Yes, and the well organized foreign groups would have been likely to teach them how to improvise high explosives from very widely available things in the USA. Some less stable than others, but all much more powerful.
The lack of such training or material in the explosive (assuming that is the case) is more suggestive of a lone wolf, which could in fact being even worse for us. Because there is a higher percentage it will be some non middle eastern US citizen that will create more of a focus on restrictions of citizens versus a focus on such terrorist groups.
From video evidence of the blast I would determine it was a low power explosive.
If the media is to be believed and it was pressure cookers in black duffel bags, the strong container and weak blast does point heavily towards something like such powder and nails.
The Boston area is also one of the most educated and influential parts of the country and with dense numbers, if they are emotionally mobilized towards nationwide restrictions it would be a good battle to defeat them.
Quickly joined by New York, and then all the gun grabbers if they see an opportunity for any type of greater restrictions on arms.
In the shorter term it would also probably result in a powder buying panic, and whatever is left not already bought from the ammo panic would probably be sold and back ordered for months.
Oops I may have just started the powder panic of 2013.