[sybren]

I don't think the kit lens has a larger aperture than f/5.6 at 55mm. Please note the difference between "aperture" (the hole itself) and "aperture number" (the ratio between the focal distance and the diameter of the aperture).

You can determine whether it's a focusing issue (as you seem to suggest in the thread title) or something else, but that requires a more controlled environment. Try setting up your camera at home on a tripod. Place it in front of a table, with the lens just above the table surface. Aim it at some clearly recognisable point at the middle of the table. Now aim the central focus point on that point, auto-focus and shoot. Now you can check the photo on a computer and see whether the point is in focus, or whether the focus lies in front of or behind the point you focussed on.

If it's not a focusing issue your entire photo will be blurry/soft. If it is a focusing issue, something will be in focus.