On safari this year I had my camera on a ledge just behind the driver's seat. Was perfect place but, for some reason, whenever I picked it up I would move the mode dial, normally from Av to M. A real pain when I didn't notice, especially when a leopard walked past.
But I do like being able to instantly switch to C1 and C3 - which I have setup, one for movies, one for emergency default shooting. It would be nice to have the locking optional.