Personally I judge peoples ability not on knowledge but on willingness to learn as that is the key to knowledge.
I like Plato's comment I know that I know nothing as it's a good way to view yourself, as that way you can always learn and it avoids you believing you know it all. Think of it this way I've took courses in things that I am very proficient in and most would probably say I don't need to do that but it's those people that don't realise there is always something you don't know that benefits you greatly.
Biting the hand that feeds IT
