First day was somewhere around Mar 25, last day is about May 20.  Ideal is probably Apr 1.  For our operation, I do not see any intended corn acres being abandoned until at least the last day to insure corn.  The corn CRC is just too good for our beans to compete. 

Planting near the last day I would estimate the chance of an insurance claim at 50% or so, but that's just a sophisticated wild-assed guess.