Several replies were given. I like the one given that said:
what about the biblical commandments to cover? (Cor 11:1-16, 1Thess 2:15, 3:6)The bottom line seems to be this: "Technically, yes, head coverings are mandatory. However, for the sake of economy, they are often (too often) dispensed with."
In summary, the reasons St. Paul advises women to cover their heads in church are:
1. Our Lord commanded it;
2. it is a visible sign of an invisible order established by God;
3. The angels at Mass are offended if women don't use it;
4. it is a ceremonial vestment;
5. it is our heritage.
And I can see the application here to all who call themselves Christian.