10-22mm image quality problem

I have a new 10-22mm for my 40d and I think it might be defective. The image quality is not what I would expect from this lens. Also, when manually focusing at infinity it is blurred but when I focus in a bit it sharpens up. Here are some sample pics shot on a tripod. Highest quality Jpeg, AV at F11, Stardard picture style. First three shots are at 10mm, 17mm, and 22mm. the last is with the kit lens at 28mm. All shots are autofocused on the tree trunk in the center of the pics.

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You should post a 100% crop...

It looks to me that over-exposure is more a problem than sharpness. Over-exposed images may look like they lack sharpness. To really test a focus issue, you may want to find another subject like some inscriptions on a wall, etc.. Do you have another lens like a 17-85 or 18-55. You could compare one of this lens with your 10-22mm at 17mm/18mm.

In my first post the last shot is with a 28-135 kit lens. the first 3 are with the 10-22. Here are some 100% crops:

10-22 at 10mm

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1. Because this lens is so wide, it will seem like it isn't as sharp because there is so much in the frame compared to other lenses when you try to blow it up and look at fine detail. Many people complain about this. That is the way things work if you want a lens this wide.
2. F/11? I'm pretty sure you will see some diffraction there, but I'll wait for an expert to chime in.
3. Use the lens like you actually would. Real world test shots will tell you if the lens is working for you or not.
4. Infinity on the focus scale isn't at the end of the focus ring travel.

I am also betting on the overexposure. It can easily through everything out of balance in an image.
I used a 10-22mm for a week or so a little while ago, loved it, but you can't really expect huge sharpness from a uw-lens. And the ultra wide shots are rarely cropped so you actually don't need much sharpness. IMO.
The new 11-16 f/2.8 Tokina is looking promising in sharpness though... But seems to have huge variety between lenses.

Thanks for the explainations. I just need some practice using this lens.

This is what made me think there was something wrong with the lens. It is explained in the owner's manual which I just now read. Lesson: read the owner's manual even if you think you know everything.