Usage of なの

Politely I could say Bob はどこですか。 or Bob はどこなのですか。 Less politely Bob はどこお or Bob はどこなの（And i could probably omit the　は too?) The なの does not appear to change the meaning at all, seems entirely superfluous. But there is probably a nuance :-) - and its apparently rather, but not strictly, female usage? Any comments on the usage & implications of nano (other that 10^-9) welcome.