I guess I'll be the one to get this thread started.
Quick & dirty macro test with the EF 24-70mm f/4L IS on a 6D body. I also tried the same shot from the same spot with my 5DmkII and when I looked at the exif the focal length registers as 80mm. Weird huh?
CRKT by Abram Goglanian, on Flickr
1/160 @ f/5.6 ISO100