The Boston murders and the Nutty right
(1) Speculating that Muslims did it;
(2) Outrage at the non-wingnut media and internet for speculating that domestic right-wing extremists did it;
(3) Fuming at President Obama for not using the word "terrorism" in his first public statement on the subject (to their credit, PowerLine dissented).
I actually have no problem with (1) -- discussing such possibilities is perfectly legitimate as long as one makes it clear that it's just speculation -- but it makes (2) hypocritical.
Besides what I call the "Sane" and "Nutty" factions of right-wingers, there is also a smaller "Super-Nutty" faction, the Ron Paul cult. Among these quintessential loons, the dominant meme seems to be that the Boston bombing was a "false flag" operation, something faked or staged by the government for some obscure but nefarious purpose (see for example here and here including comments, and also here and here). Of course such insanities also erupted after Newtown and, notoriously, September 11.
Personally I wouldn't be surprised if it turns out to be Islamists or right-wing extremists, though I think the latter is a little more likely, given the April 15th date (taxes are a huge red flag with some of those people) and my sense that Islamists, unless locally-based, would be more likely to target New York or Washington. But it's really impossible to say yet. It could even be some isolated mentally-disturbed person with only a tenuous connection to any particular agenda.
I want to close with this already-widely-cited posting by Patton Oswalt. Please do read it -- it's something we need to keep in mind at such times.
Update: Snopes has a handy review page on the various myths and stories which have already begun circulating about the bombing.