This comes up from time to time but it's worth repeating for the newbiews out there...
Photographers: please try and credit your models. This is after all a 'networking' site, not just a showcase for your talents.
Models: insist on the photographer crediting you - it helps get you more work.
I know there are various reasons models wish not to be tagged, but a simple 'ABBIE_C, Model not on MCM' or 'Model name witheld by request' isn't really much of an effort is it? This can be put in either the 'model' section or in the caption field.
Otherwise it just seems a bit like those strange guys who get overly protective of their subjects... Perhaps they don't like sharing models because they fear other guys doing a better job than they did...?