Having had a 35L with various back/front focus issues I finally got it sorted. Even then I was never 100% happy, it just wasn't sharp enough (for me) wide open.
I've recently bought a 24L II and I am so happy with it. At 1.4 is it as sharp as it is at 2.2. I couldn't be happier, until I noticed the CA I was getting. My initial thoughts were, it's no big deal and easily removed in PS. However, I've started to reconsider this. Yes I can remove it in PS, but why should I, I've spent an incredible amount of money on this lens and it should be right, shouldn't it?
My worry is that if I send it back to Canon the focus might not be as good as it currently is, maybe I'm not giving Canon enough credit, but that's what bad past experience does.
I'm using it on a 7D (also in warranty) and have found that you often have to focus twice to get it spot on, something I have seen mentioned before. this isn't really my issue, but if I do decide to send my lens to Canon I may as well send in my 7D too.
I Just wanted a little advise as to whether this sort of CA is acceptable on this lens. The attached photo is a crop and shot at F1.6.