The 24-105 Canon F4 IS lens is a fantastic standard zoom lens. It is wide enough for most cicumstances, and gives a much longer reach than the very well respected 24-70.
The addition of image stabilisation gives many advantasges, including a huge rise in image quality from DSLR, such as the Canon 5D Mk II and Canon 7D.
Phillip Bloom has stated this is one of his favourite lenses. It is lighter and shorter than the 24-70, and on a crop factor lens has a similar image quality.
Even though F4 is slower than a standard F2.8, the background blur achievable at 105mm at F4 is almost the same as 70mm at F2.8. The low light performance of modern cameras such as the C300 is so good that F2.8 is often unnecessary and in many circumstances gives you an unusable depth of field.
We use this lens and the 24-70 and have found strengths and weaknesses to both lenses.