I haven't got any diamond camo. Got about nine or ten weapons gold but no diamond. Why? Because I only use weapons I like. The only category I will get diamond is the LMGs which in BO2 I like all of them. Certainly wont be getting SMGs and doubt I will do assault rifles either. So if this means I lack skill, so be it, not really fussed.
I don't even have Gold camo on any of my guns (I don't feel a need to get every one), but even if I did have Gold and/or Diamond camos, I wouldn't use them because, to me, they're both pretty ugly and are more for just unnecessarily showing off than anything (people having some impression that they're really "skilled" by getting them, even though one can simply grind and get them eventually).
diamond camos got old fast.. really fast. I mean it was something different at first.. and then you realize you're running around with a gun designed by ed hardy. yup, your gun is bejeweled. how incredibly tacky. think about it, your weapon 'shines bright like a diamond' .. lol, had to throw that one I there.
I've gotten diamond for some of my classes, but to be honest I use art of war or ronin the most. they can somewhat blend better with the surroundings.