Regarding the softness - it does seem that some 10Ds/lens combinations are affected by focus problems. This has been fairly conclusively documented over on Dpreview, and while many user complaints can be written off as "user error" this issue does appear to have some basis in fact.
The first thing to determine is whether the lens or camera is at fault. You'll need a 2nd lens, a tripod and a test target. Compare results using AF
with both lenses. If both lenses consitently mis-focus on AF
, the camera needs adjustment, and should be returned to Canon (with the images and test procedure as evidence). If only one lens shows a problem, then it is the lens that needs adjusting. If, in this test, you get perfect results, then you will have to accept that perhaps your technique is at fault.
Colin K. Work, Pixstel