Canon 70-200mm F/4L IS USM Review
Popular Photography has an excellent review on this lens. The shot at right was taken handhold months back in San Francisco at 0.04 second with focal length as 150mm. I am pretty happy with its optical performance and IS performance. Besides, it is lighter than its f/2.8 sibling. My neck felt much better after wondering around San Francisco for the whole day. 
Here are fascinating reviews around the net on this lens:
