when i tested the copy in the shop on their body i noticed it was front focusing it was definately off compared to their demo but not massively
after micro calibration on my cameras ended up +13 on the 5D mk2 and +6 on the 1D mk3, it was the last new copy they had at that price, i could take it back and exchange it for the store demo copy which seemed to be less off, doesnt really bother me as all my cameras have micro adjust but i think if anyone tried this lens on a camera without micro adjust it would upset them
would you swap it out for the demo which would most likely need less adjustment? as it is on my cameras I have the focus bang on now, pretty impressed, it is really really sharp
If you had a 60D, you'd be screwed. Thus, the complaints about Sigma lenses. With some exceptions (like the Sigma 50/1.4 with focus shift), AFMA can correct many of the problems (at least the systematic ones, reportedly there are inconsistent issues with some Sigma lenses, too).
As for taking it back, +13 is a pretty hefty adjsustment. You are running the risk that if you get another body someday which is further off in the other direction, +20 might not be enough to correct the mismatch.