[font color=\'#000000\']There have been many "reported" problems of "Back focus" issues with the 10D. These are listed ad nauseum on the 10D forum on dpreview.com. But beware...
1) The main thrust of that forum is to whine about every camera, feature, manufacturer. Oddly, every DSLR at some point is claimed to have major focusing problems by someone. They even bitch about the poor focusing of the 20D, a camera that hasn't even been released yet.
2) If there really is a problem, Canon would deny it. Send it in for a true evaluation.
3) I have a 10D. My images are sharp as a tack. I manually focus and have middle age vision.
4) I use "entry level" Canon L glass (17-40/4, 70-200/4), so I cannot speak about the merits of the EX Sigma stuff, really. I bought a middle priced Sigma zoom about a year ago and sold it after a week. I immediately realized just how important the glass was. Jonathan may make a good point.[/font]