I think Joe is wrong here  with regard to the EFS and the 5D as the rear elements of the EFS lens protrude into EFS mounting if you try them they can foul the mirror and result in expensive repair bills.. Canon are quite clear that the EFS range of lens are only suitable for the cameras as stated.. The EPS size as little to do with it as in fact the 10D will also not function with these lenses as it too has not had the camera internals modified to fit the EFS lens, the mirror and Prism has had to be modified on cameras like the 20D and 30D, which have a less bright viewfinder..

Danny O'Byrne  http://www.digitalartzone.co.uk/

"All the technique in the world doesn't compensate for the inability to notice" Eliott Erwitt