After goggling the 24-105 I ran across a post about it being blurred when it was used at slow shutter speeds. The tests were done at 1/5 shutter and F4. Another shot was taken at 1/5 and F5.6 and there is a noticeable difference. It looks like it is a problem with newer lenses. My 24-105 was delivered a few weeks ago. Here are my results. It should be obvious which image was shot at f4 and which one was shot at f5.6. Both shots are with IS turned ON. From what I read Canon will fix this issue. I am not happy about having to send a 2 week lens back for repair, but it will give me some time to play with a few others.
Donald in Long Beach CA
EDIT - Apologies if this has been addressed. I searched but didn't find anything.