I love my EOS 40D as a camera for action shots. The 6.5 frames per second (or only 6 according to some tests) are a huge benefit when doing action shots. Take this shot for example:

EOS 40D, EF 4/500L IS, 1.4x extender, tripod

The wing beats of the duck (a female mallard) are very fast. The more frames per second your camera can shoot the higher the chances you get the duck with a wing position you like. That’s just simple math.
The number of frames per seconds has constantly improved with Canon prosumer models. My old EOS 10D had only 3, the 20D and 30D had 5 and the new 40D now has 6.5.
Together with a fast lens and the fast AF system of the 40D that camera is a very good but affordable tool for action photography