I don't think March 2013 is likely. Tick-tock has been closer to a 14-month cycle than yearly:

07/2006 - Conroe
10/2007 - Penryn (15 months later)
11/2008 - Nehalem (13 months)
01/2010 - Clarkdale (14 months)
01/2011 - Sandy Bridge (12 months)
03/2012 ? Ivy Bridge (14 months)

While the ticks had taken 14~15 months to come out, the tocks had taken 12~13 months. With Haskell being a tock one might expect April 2013 to be a likely launch date, but I think May 2013 is a better guess. Both previous tocks had market pressure to push up their launch dates. Nehalem added an IMC to capture the Server/HPC market where the Opteron was still competitive. Sandy Bridge's IGP was a vast improvement over the inadequate GMA that Apple found unacceptable. But what's Haskell's killer feature? Sure, it may further improve the IGP, but I think with Ivy Bridge the IGP is already good enough. Lacking market pressure, I believe Haskell will launch closer to May 2013 than April.

In any case March 2013 is very unlikely.