The more I think about the 24-70 f/4 L IS USM the more I like it.
Disregarding image quality the main features for a comparison are focal length, aperture, maximum magnification, and stabilisation.
The 24-70 f/4 is worse than the 24-105 f/4 for focal length, but better for maximum magnification. Now here's my take:
In practice, when not using the macro, I am often MM limited or focal-length limited, the difference is that an MM of 0.7 could often be enough, whereas in situations where 70mm aren't enough I often need more than 105mm, too, so the 24-105 is of no real advantage.
I actually have the 24-70 f/2.8 I now, which I got over the 24-105 for the larger aperture, but since I've got a couple of fast primes this isn't half as important as it used to be.