Received this lens today. So far it looks great.
Here is a shot hand held wide open @200mm @1/10s. Looks like the IS works great.

IMG_0002 by clemmb60, on Flickr

Camera Model: Canon EOS-1D Mark II N
Lens: EF70-200mm f/4L IS USM
Focal Length: 200mm
Aperture: f/4.0
Exposure Time: 0.100 s (1/10)
ISO equiv: 3200