I agonised over the choice to buy this lens as a replacement for the 28-135 on my 40D, as I was concerned about some of the quality issues raised affecting performance, given the rather high cost of the lens.
The 28-135 has proved to be a good reliable lens but had always left me wondering 'is it me or the lens'.
Straight out of the box, the 24-105 left me in no doubt that the 'softness' of my previous image where a thing of the past. At f4 and in fading light, a few random shots were just beautifully sharp with so much more colour and contrast than I had experienced before.
The build quality is what I would have expected from an L lens.
This lens will remain firmly fixed to my 40D for a long time to come