Okay it is ghastly but I am always a little hmm when people use Dr outside of work. None of my doctor friends ever do only a friend with a PhD does.
Well, that will be because your 'doctor friends' are technically only 'doctors' at work. They are doctors, like a plumber is a plumber, because doctoring is what they do. It isn't actually their title. That's why consultants become Mr/Mrs/Ms again, because they are no longer doctors. Unless they have a PhD ;)
Whereas a person who has a PhD - their title IS doctor. It refers to something that is inalienably about them, isn't transferable and doesn't change whatever job they do. For women especially, it's certainly a far more relevant way of titling oneself (if applicable) than marital status. No-one needs titles, they're redundant in modern society, but until they fall out of use, a person with a PhD calling themselves by the title 'Dr' is just as sensible, if not more so, than someone changing from Miss to Mrs simply because they signed a different bit of paper.
It's a shame that being a medic and achieving a doctorate use the same words to describe them, but far more depressing is the inevitable chippiness that pops up (which always, and so stupidly, sneers something along the lines of 'proper doctors', referring to medical staff) whenever PhDs are mentioned. It's baffling - I don't think it happens outside of the UK. Perhaps they'd all be happier if we all referred to one another as 'Plumber Smith' 'Optician Johnson' 'CallCentreOperative Clarkson' and the like 