"When is the Canon EOS 5D Mark III going to be announced?" is the big question hitting my inbox these days. And that is a good question - one that Canon has not answered publicly.
Last year, my guess was that the EOS 5D Mark III would be announced in August 2011 with availability in December. The reasoning behind this answer was that the Canon EOS 5D Mark II was announced 3 years after the Canon EOS 5D and August is historically the month of one of Canon's biannual major DSLR, lens and flash announcements. The 5D II became available in December (to those who preordered early).
Today, I'm much less optimistic about seeing a 5D Mark III this year.
First, the Canon EOS-1Ds Mark IV announcement did not happen in its historical timeframe (August 2010) - and has not happened to date. I expect the Canon EOS-1Ds Mark III to be updated before the EOS 5D Mark II.
And second, the disaster in Japan was hugely disruptive. Details of Canon's recovery have been absent lately, but I have not been hearing any optimistic news coming from the affected area. I'm happy that we can still buy most current Canon DSLRs and lenses.
So back to the question: "When is the Canon EOS 5D Mark III going to be announced?" As with the rest of Canon's unannounced products, no one who knows is allowed to say. My complete guess is that we will not see an upgrade to the 5D II available until at least mid-2012.
The advice I've been giving is to get the incredibly successful Canon EOS 5D Mark II now. It has impressive image quality and you will most likely get a LOT of great shots from it before even my last-year-estimated 5D Mark III arrival date.