Alex,
I found that it was important to keep the shutter speed as high as possible. The first of the images I posted above (the breach) was shot at 1/500. It was ok, but I felt that and other images shot at that speed weren't freezing the action (esp. the water droplets and spray) enough. The next shot (lob-tailing) was shot at about 1/750).
After reviewing those images, I kicked the ISO up to 400 to get faster shutter speed. Once I switched to the F100 (the raised flukes), I mostly used Provia 400 film, aperture priority at max aperture to get fastest shutter speed I could, usually 1/1000 or better, which I think worked best.
My experience was that the ability to handhold this lens at relatively slow shutter speeds was only useful for shooting fairly static subjects - animals in repose - on land, ideally using a monopod (or a tripod in "monopod mode"). As you say, it's not camera shake - dolphins, whales and similar subjects are just moving too fast.
Even if the subject isn't moving, I found that it was very still very difficult to keep the camera aimed at the exact same place when shooting from/on a boat, especially at longer focal lengths. Essentially, the camera/lens is panning, and the VR system can't cope with this.
Shutter speed was particularly a problem with gannets, which are moving very fast when they're dive-bombing the sardines. You needed at least 1/1000 or even 1/2000 to avoid blurred birds. Interestingly, it was iimpossible to see with the naked eye how the gannets folded their wings in close to their bodies at the last milliseconds before striking the surface of the water. It happens so fast that they seemed to go into the water with their wings still extended out. E.g.,
