Since no foreign terrorists are taking credit for the Boston bombings, I believe that the bombings are the result of domestic terrorism. When foreigners choose to be terrorists they usually let every one know some way such as the Internet or television, and since that did not happen this time I think it is domestic.
I don't think I have enough information at this point to make a decision. It may even be that nobody really knows yet. If I absolutely had to choose, I'd say that, based on the small scale and the type of event, it was domestic, but this is only if I am being pressed for an answer. I only hope that these attacks will not lead to further discrimination against any group of people, whether that be a racial group, the mentally ill, or anyone else.
The bombings seemed much smaller scale compared to other foreign acts of terrorism, especially compared to 9/11. The fact that the bombing was very localized lends credibility to the belief that it was a lone-wolf type, domestic act of terrorism.
The fact that no source in the international community has stepped forward claiming responsibility also makes it more likely that it was domestic.
I would have to say that I think the Boston Bombings are an act of domestic terrorism and not foreign terrorism. So far, all evidence that is available and has been released to the public points to a domestic attack. I think that Al Qaeda would have claimed responsibility by this point if it had been them.