The Really Right Stuff B5D-L bracket is my third bracket from RRS. RRS Makes custom brackets for cameras and lenses that fit into Arca-Swiss style clamps. I fell in love with their products when I bought my 20D bracket, due to the amazing quality of workmanship and the fit and finish. I have been very happy with my 5D bracket, except for one thing that I recently noticed. The bracket wasn't touching the the side of the camera and so in portrait shots it could flex or vibrate.
I called RRS today and talked to Joe who was very helpful, he told me I could loosen the screw and push the bracket over a tiny bit in order for it to touch the side. It worked, although it is only barely touching the side of the camera now. The 20D bracket made full contact along the side of the camera body and was much more solid. He noted that although their tolerances where very tight, within 5 thousands of an inch, the outside of a camera body may have larger variances. He said I could send it in and they would look at it, but because they are located in San Luis Obispo, asked if I could drop by some day and take a tour of their shop and have him fit it to my camera, which he said would be fine. He also said that they would be working on a fix for this in the next version. I'll let you know what happens when I go.