hmmm...
This is probably jumping the gun a bit, but are you noticing that the point you focused on is blurry, but another part of the image is in focus?
The lens may be front / back focusing.
This is when the lens is actually focusing slightly in front of or behind the target spot.
here's a quick test:
- Take a ruler out.
- Put camera on tripod.
- Shoot it at an angle, focusing on a specific number.
- See where the photo is actually in focus.
Here's an example with an image i found (not my photo). if you focus on 20 and in the final image 21 or 19 are sharp and 20 is blurred then your lens is likely to be front or back focusing. You will need to send it to Canon for a recalibration.
This type of test may be premature, but it is free, quick and the results may give you peace of mind to know your gear is to spec.
Then again, if it passes this then it likely means you are to blame
(but your technique is easier to fix then the camera).