This spring when I cycled my gear through Canon for cleaning and maintenance, one of the perks of being a platinum member of Canon Professional Services, I had them make a slight modification to my Canon 5D mkII as well.
I had them replace the standing mode dial with a locking one – now a standard feature on the mkIII. Now I’ve heard some people call this the most useless feature of the mkIII – but for me it really does help, and this is because I use various “Black Rapid” straps to carry my cameras on a wedding day. The Black Rapid straps attach to the tripod socket and carry the camera upside down hanging at the side. This configuration allows the weight to be carried by the shoulders instead of the neck with a normal strap – something that after 8-10 hours does make a difference.
Without the locking strap the mode dial would occasionally get moved just by brushing against my slacks while walking – nothing like having your exposure all set and then finding it in the wrong mode when you go to grab a shot.
If you’re shooting the mkII and use a sling system for the strap – this is an upgrade I highly recommend.