One has to be careful when using long lenses. Vibration and shake are greatly magnified.
In my case, I haul out the Bogen 3033/3057 setup and strap the long super zoom to the head. For stationary subjects I can clamp the controls down tight and either trigger the shutter using the 40D's 2 second delay, or use my new 2.5foot tethered trigger.
For birds in flight (BIF) I found that loosening the tripod head controls (horizontal and vertical) just enough to be able to move the camera setup is very usable. I realize it might be counter-intuitive, but using the tripod in this manner allows me to keep the focus point fairly steady on the subject. I have now shot thousands of images using this method and have better results than with trying to follow a BIF handheld (camera/lens off-tripod).
As for the lens being sharp? Oh yes, it most certainly is sharp. Much sharper than I anticipated, in fact. After reading all the mis-leading comments over on DPReview I had to steady myself and come back to reality. The 100-400 f/4.5-5.6 L Canon lens is simply superb.