For military personel it is treason, for anyone else it is not. Especially when the group releasing the documents are not American, they have no duty to keep the secrets of foreign nations. Heck, you are not required to keep the secrets of your own goverment either. When the pentagon papers were published by the New York Times, and Nixon had them taken to court, the supreme court found 6-3 in favor of the New York Times publishing the documents.
"Only a free and unrestrained press can effectively expose deception in government. And paramount among the responsibilities of a free press is the duty to prevent any part of the government from deceiving the people and sending them off to distant lands to die of foreign fevers and foreign shot and shell."
So in the closest case we have to Wikileaks, the supreme court ruled it was the newspapers RESPONSIBILITY to report the lies of our government to us. If you want to hide your head in the sand, obey big brother at all times, and never question your government, move to to China, they appreciate your kind there. America was founded on the idea of an open democracy by the people for the people, not some secretive government that disappears people who disagree with it for "treason". But the reason the governments are scared of Wikileaks is because a lot of people in government do things that if their people found out, would have them thrown out in seconds. Every time wikileaks releases more documents, the government starts banging the treason drum, saying it puts our troops at risk. As of yet not one single Wikileak can be blamed for causing the death of an American soldier. They said the same thing about the Afghan war document leak in august. The secretary of defense himself said "the review to date has not revealed any sensitive intelligence sources and methods compromised by this disclosure." Those were military communications, and these are diplomatic cables, which are far less likely to endanger troops, and far more likely to embarrass two faced diplomats who are being caught saying one thing to the public and another in private.
The truth of the matter is 911 was an incredibly successful attack on the freedoms of Americans. No group had ever been as successful at changing American views and ideals since the founding fathers. Since then large portion of Americans can be herded wherever the government wants you by using words like "National Security" and "terrorism", people willingly give up freedoms that our grandfathers fought for and often paid for with their lives. That one attack did more to bring us closer to a 1984 style big brother controlled America, where any dissent is crushed and called treason, than any effort by any group. People willingly give up their freedoms and rights in exchange for protection from the terrorist bogeymen. Hell they don't even need to get actual protection, most people are perfectly happy with the bullshit security theatre their goverment puts in place (at great public cost) that will do nothing to stop another attack. America may once have been the land of the free and the home of the brave, but it is quickly turning into the land of the totalitarian democracy, the home of cowards who hide behind their governments skirts.