I use the canon 100-400 lens,works great with the IS on (mode2) for panning shots.
For photo's taken from behind or head on I have variable success with the IS on.(you not really panning)
What is the best for such photo's ,IS on or off.
I mean photo's like this
Photo © Magnus Trippler
Photo © Peter Unmuth - VAP
[Edited 2005-03-24 20:37:54]