The United States Department of Justice has given twitter a subpoena asking for the details of 'customer or subscriber accounts for each account registered to or associated with WikiLeaks', from November 1 2009, or over a year ago. You can read the subpoena in more detail here. The reason: it [the information] is 'relevant and material to an ongoing criminal investigation'.
I'm unclear as to what precisely 'associated with WikiLeaks' means, but I'm under the impression that the subpoena applies to every single one of WikiLeaks's, as of me writing this, in the region of 635,000 followers (although, presumably, there are SpamBot followers).
Although I'm not an expert on US law I am under the impression that only the stealing of state secrets is actually illegal, making the criminal investigation either tangentially towards Julian Assange or towards Private Bradley Manning, who is believed to be the one who provided WikiLeaks with the material for the Iraq War Logs and Cables leaks, as well as the 2007 video taken on an Apache helicopter which showed (I think) civilians being shot dead by it. I doubt that the data would be material to the allegations against Julian Assange (which he may actually be guilty of, but he may also be innocent and it is the latter which would normally be assumed (most likely for the worse, but there is little doubt that who Julian Assange is is the main motivation for the efforts to charge him, not the crime itself (this being a sad reflection of our time))) due to them being unrelated with WikiLeaks except for the man these allegations are towards, nor would knowing these details be material in any investigation towards Private Bradley Manning (who is presently being held in solitary confinement) especially considering that he has spent most of the last year imprisoned.
In fact this is likely just another stage in the US Government's attacks on the organisation; making people afraid to support it, to quote @Nick4Glengate "They don't need to charge us with anything - they are relying on fear.". Of course there is one other advantage I can think of that the US government would have; the information on more people, people with whom they may not agree politically. Knowing that the US know who you are is actually terrifying, meaning that they get two advantages which enable them to better control us; knowledge of who we are an us being afraid of them. I believe that this can be classified as tyranny and almost certainly violates the US's own Constitution (though whether this is viewed as an issue by the government remains to be seen).
This brings me onto the second part of this post; yesterday, by some coincidence, I was reading a 'book' (well, a PDF version of a book) by Cory Doctorow called "Little Brother", I won't spoil the details of the plot here (although, if you want to read it, it's available free to download off the official website, I personally picked the fan-made PDF), but a blog is started in the book called 'Abuses of Authority' which details the 'Big Brother' actions of the Department of Homeland Security, and abuses of power. I'm thinking that we need something like the the one in 'Little Brother' to keep an eye on not only the 'Big Brother' circumstances which can arise in this country, like as detailed by Police State UK amongst others, but the ones in other countries, such as the US, all in one place; I'm of the belief that, if dots can be connected (to use a term similar to that used in the 'about' section of Police State UK) between the various attack on our civil liberties by the ruling class in the UK then those same links can be made with other countries, and if we are going to tackle the 'Big Brother' complex in which many countries have settled then it must be a more international co-ordinated effort which stops it, if we're being oppressed then it's our right to stand up to our oppressors, and we should stand up against all oppression, not just that which effects us.
Incidents like this abuse of power by the US DoJ are precisely why I think we need a collaborative effort to detail abuses of power wherever they happen, not just in places such as China (which would almost certainly be lambasted for pulling a similar move), but in ostensibly 'free' countries, such as the UK and the US, where civil liberties are being excessively curbed in the name of security.
We need to show our governments (as, to paraphrase the Constitution, Government comes from the consent of the people) that we won't stand for this sort of thing, regardless of whether it occurs in the place we live or overseas, whether it serves the interest of our countries or not; isolation between peoples of different nationalities serves only the interests of those in power, enabling them to get away with things they ordinarily wouldn't by stirring up fear of people in those countries and making us feel that, for our safety, our liberty, and the liberty of others has to be taken away. We need to collectively make a stand against and spread awareness of these abuses of power, otherwise they'll keep happening.