I certainly read doubts about the AF, especially off the center point.
However, the effusive praise, perhaps well deserved, won't light a fire under Sigma to address the AF problems.
My experience with the lens is that the AF is rock solid on the 5D3, not quite as good but close to the consistency of the 24-70ii. On my 1D3 and 1Ds3 however the AF is complete and utter garbage.
Bodies: 1DX,1Ds3,5D3,X-T1,A7R,E-M1 Lenses: 12.40 2.8, 16-35L F4 IS, X 18-55 2.8-4, Σ 35 1.4 A, 35 2.8 FE, Σ 50 1.4 A, 24-70L II, 85 1.8, 100L IS, 135L, 70-200L F2.8 IS II