After reading the reviews on this site I expected to love this lens. I don't. I've had it for 6 months or so now and It's good...but images need a lot of post-processing and sharpening, at all apertures.
Perhaps it's because I'm comparing it directly with the 135L which I bought at the same time and is awesome...and I've just been out with my 50mm 1.8 mk1 and I realise that it all comes down to image quality! 0.3s autofocus speed (or whatever) isn't an issue for most of us.
Perhaps I've got a bad copy, but I get tired of hearing that as an excuse. If you buy a TV you don't expect to have to change it for one or two copies. If Canon have QC issues theni it's 'more-fool-us' for tolerating it!
I will keep the lens...and keep plugging way with it. Hopefully I can change this review for something more positive.