Funnily enough although I use the 24-70 lots for work I can't say I'm a big fan of it. Personally I find when focusing using an off centre focal point the sharpness is not good. It's one of the few lenses where focus and recompose works better for me than selecting an outer focal point.
For me I think it's superb in the middle but not so good off-centre.
Of course I might have had a poor quality copy. As it's recently been stolen I guess I'll be able to compare the replacement to the old one and then I'll find out