As always with something like this - the 24 hour rule is in effect.
From the Anti-Mullah:
Khamenei has died. The formal announcement is expected to be made tomorrow morning (Tehran time). Relative to this, all regime organizations including the official regime news agency "Seda va Sima" are being draped in black.
Michael Ledeen at Pajamas Media speculates:
His condition had already seriously deteriorated over the last months, aggravated by his nervous condition due to  his inability to solve the problems created by his manipulation of the election results and the refusal of [a large part of] the population to accept this, plus  his loss of religious authority by means of the repeated condemnations of events by senior clerics
Reportedly the principal aims of Khamenei of the last couple of weeks, if not months, were to ensure  a positive reputation as his legacy and  the physical survival of his family members and their wealth, reportedly now largely in Syria and in Turkey (remember the truck convoy of $8.5 billion in cash and gold that was seized by the Turks?).
Outlook is uncertain but speculation is – considering that he is in coma since more than 24 hours – that he may not come out of his coma and/or that he may die very soon.
If he dies it is expected that immediately a bloody clash will develop between the powers behind Rafsanjani, who will immediately claim temporary religious authority and overall control, and the powers behind Achmadinejad who will scramble in order to regain control and ensure their survival.
Update: 5:30 pm MST - Still no definitive word on the Ayatollah's condition but Ali Alfoneh is saying:
Rumors that Iran’s Supreme Leader, Ali Khamenei, has died began circulating yesterday in Tehran’s bazaar. Today, Iranian bloggers report an “abnormal atmosphere in the city” and increased presence of plainclothes agents in the capital. Such rumors circulate from time to time. Obviously, every rumor about Khamenei’s death to date has been false, but the ferocity of the rumors both reflect the opacity of information about Iran’s decision-making class, and the wishful thinking of a public that blames Khamenei and his cohorts for betraying the promises of freedom and democracy which underpinned the revolution.
Read his take on what could happen if and when the Ayatollah kicks here. (God willing.)
What the heck. It's getting into gossip territory now!
Update: 9:56 pm MST - Beliefnet.com wants to pursue the tweets but Twitter is down. Oops! Twitter is back up and the rumors of Khamenei's demise are being removed from Wikipedia.October 15, 8:15am MST: Latest updates can be found here.