I own it and use it for shooting weddings after giving up on the 24-70L due to 3 bad copies.
My first copy was horrible. This present copy is very good. Extremely sharp, perfect focus, strong, even harsh contrast (not great for people, good for everything else).
The 24-105L is known for it's bad distortion and vignetting at the wide end and questionable bokeh throughout. The vignetting actually works for me with wedding work and isn't a problem for my stitching. Not that hard to fix anyway. I use PTLens for the distortion and primes for when I need decent Bokeh!
What it is however is a very sharp walkaround lens with a aperture faster than anything else with the same range, a 4 stop IS (though no mode 2, allow it to settle if you focus recompose and switch off on a tripod!), weatherproof, etc, etc.
I was using primes for my stitching work but came to the conclusion that the zoom was more convenient when I had more resolution than I could print anyway and the results really are very sharp. These two pics were shot with the 24-105L, both stitched, both razor sharp.
Just to reiterate, there are incredible copies of this lens but I'd say that at least 50% are not so great so make sure you can test the heck out of it first. It should be almost prime sharp!