I've never noticed it with my M4. My Zeiss Contaflex however, does have a nice leather smell to it.
BRB, smelling my camera...
Ok, I smelled some of my cameras, and didn't find a smell on either of my Leicas (M4 and IIIC sharkskin). My Contaflex has that nice leather smell, and my 1947 Kodak Flash Bantam even more so.