Mmm, I forgot to add in my example I was talking about.
Anyway, this is 7D, EF-s 15-85 @ 15mm, f/14, iso400, 1/60s (ok, maybe too high f and iso, but it's one of the first shots I took with my camera when I got it, specifically to try out the CPL), and a Fujiyama 72mm CPL.
No marks for composition on this probably, it was only a test shot.
You can clearly see the blue banding directly in the centre of frame, but it's not "bad" by some definitions, at least it's not distracting or annoying.
No idea where the sun was, but it was taken at 10am in Europe Summer Time (presuming i'd set the clock correctly), I've checked a map
and I was facing roughly NNW, so sun is just behind my left shoulder if not directly behind me.
So given how noticeable it is here (24mm FF), it's only going to be noticeable even wider, in fact I just bought the Sigma 8-16mm because I didn't care about not being able to put CPLs on that huge bulb of a front element.
Facing perpendicular to the sun gives you a better CPL effect, so maybe it wouldn't be more noticeable wider then, I'm not sure...