Well, I once knew a British Arab woman who was a curator of Islamic art in a museum. She claimed to be a muslim, yet she never wore a hajib at work. She wore only western clothes, with her hair and face uncovered. I would imagine that a modern muslim would see it as optional, while those brought up in a strict sect would see it as compulsory.
I have met Bhuddists who eat meat and drink alcohol, and Catholics who use contraception, so I suppose it's a matter of making up one's own mind or being told by somebody 'this is what you must do if you are a true believer'.