Is bin Laden alive?

Angelo Codevilla, a professor at Boston U who has intelligence experience dating back to 1977, summarizes the evidence as he sees it:

Negative evidence alone compels the conclusion that Osama is long since dead. Since October 2001, when Al Jazeera's Tayseer Alouni interviewed him, no reputable person reports having seen him—not even after multiple-blind journeys through intermediaries. The audio and video tapes alleged to be Osama's never convinced impartial observers. The guy just does not look like Osama. Some videos show him with a Semitic aquiline nose, while others show him with a shorter, broader one. Next to that, differences between colors and styles of beard are small stuff.

Nor does the tapes' Osama sound like Osama. In 2007 Switzerland's Dalle Molle Institute for Artificial Intelligence, which does computer voice recognition for bank security, compared the voices on 15 undisputed recordings of Osama with the voices on 15 subsequent ones attributed to Osama, to which they added two by native Arab speakers who had trained to imitate him and were reading his writings. All of the purported Osama recordings (with one falling into a gray area) differed clearly from one another as well as from the genuine ones. ....

Also in 2007, Professor Bruce Lawrence, who heads Duke University's religious studies program, argued in a book on Osama's messages that their increasingly secular language is inconsistent with Osama's Wahhabism. Lawrence noted as well that the Osama figure in the December 2001 video, which many have taken as his assumption of responsibility for 9/11, wears golden rings—decidedly un-Wahhabi. He also writes with the wrong hand. Lawrence concluded that the messages are fakes, and not very good ones.  

There is widely varying speculation, but of course no clear facts, on how he died if he died:

On December 26, 2001, Fox News interviewed a Taliban source who claimed that he had attended Osama's funeral, along with some 30 associates. The cause of death, he said, had been pulmonary infection. The New York Times on July 11, 2002, reported the consensus of a story widespread in Pakistan that Osama had succumbed the previous year to his long-standing nephritis. Then, Benazir Bhutto—as well connected as anyone with sources of information on the Afghan-Pakistani border—mentioned casually in a BBC interview that Osama had been murdered by his associates. Murder is as likely as natural death. Osama's deputy, Ayman al-Zawahiri, is said to have murdered his own predecessor, Abdullah Azzam, Osama's original mentor.

More at DrSanity.

PREVIOUSLY, this issue has been discussed here, here, here, and here.