Ken Brown, a spokesman for Nvidia, told X-bit Labs that Kepler silicon will be available this year, but now it seems production of graphic cards will not happen until 2012. So far, we have been under the impression that Kepler cards could be arriving just in time for Christmas, even if Nvidia already had said at the International Supercomputing Conference in June that the new cards may be delayed by a month or two.
Kepler will be succeeding the Fermi architecture and use a 28 nm production process. There have been rumors that Nvidia is struggling with the 28 nm production and that manufacturing is causing the delay. Of course, Nvidia isn't commenting on the delay and no chip manufacturer would ever give a statement on yield issues anyway. However, Nvidia is under pressure of getting Kepler out on time and especially get to Kepler right. (The current Fermi architecture was delayed several times and had a less than perfect launch.)
According to information released by Nvidia so far, Kepler cards will triple the dual-precision floating point performance of Fermi and hit up to 6 dp GFlops, while its successor Maxwell (scheduled for a 2013 release) is expected to with almost 16 dp GFlops. These are big promises and Nvidia wouldn't want to miss them.