This discussion, as well as my own experience moving from a Rebel XT to a 40D to a 5D Mark II, only helps to reinforce my opinion that the maximum (well, minimum...) f-number of a given lens is becoming important largely in the area of composition, instead of actual light-gathering ability, at least for typical walk-around lenses and 'average' situations. Of course, 'average' situations are going to vary wildly by photographer, and there are definitely times when popping on an f/1.4 lens can make a huge difference. But for most walk-arounds (and the 70-200 zooms), the extra stop of light gathering ability from f/4 to f/2.8 just doesn't seem to be a deciding factor for most situations, given the abilities of the Canon's recent cameras. In my case, at least, I gladly accepted the IS, and smaller size of the 24-105 f/4L over the 24-70 f/2.8. Similarly, my 70-200 f/4L IS has been much nicer to carry around than the f/2.8 I used for several days.I guess my point is this: as cameras become better at squeezing the most out of every photon they let through the door, our purchasing decisions can become a bit more focused and a bit less concerned with trade-offs.