I am quite familiar with the 24-105 f/4L IS ... I've had one for a dozen years.You would be revealing a pretty low level of competence if you are claiming the 24-105 f/4 is anything less than an excellent, professional level lens. I'm always surprised by the lack of regard the lens gets here, though, so you wouldn't be alone. Look back through the past 20 years--and even this year!--of PPA magazine to see how often the lens was used for their cover photos. And if you could get your hands on a copy of any year's Loan Collection, you'd see how often it is used for award winning photos. Landscape and nature photographers have been using it as a reliable and amazingly flexible lens for years also.
You were just being flip, right? A little tongue and cheek to be provactive?
Pros use primes and f/2.8 zooms for a reason. I have never seen a pro use a 24-105 f/4 zoom on a job, although I'll take your word that photos from that lens are showing up from time to time. But at the end of the day, the pro workhorse lenses are the f/2.8 zooms and the primes.
I'm actually surprised at the loyalty to the f/4 zoom on this thread, maybe it's the convenience and affordability factor and it may be the only L lens that some people ever buy (because it's in a kit) in which case they would certainly be blown away by the quality.