Wanker and proud here, I'm afraid.
I use Dr as a non-gender-specific alternative to Miss/Ms/Mrs. Simple as that. FWIW, unless specifically asked for my first name, I also sign myself as Dr T. UnheardOf. I also use it when signing things jointly with my DH as a way of breaking the traditional priority of male over female, so we are Dr UnheardOf and Mr UnheardOf'sDH, rather than Mr and Mrs. (OK, so not so much smashing the patriarchy as chipping away at it with a butter knife, but, hey, every little helps!) I got divorced and changed my name back to my maiden name while I was doing my PhD, so perhaps this whole 'Dr as opposed to Ms/Mrs/Miss' thing was particularly important to me.
I have never used it to blag anything (and have never been successful in blagging anything or been treated noticeably better than anyone else) and I'm a bit horrified by the idea that it cold be used in this way. I am told, however, that the title 'Dr' can sometimes be a factor in lowering your car insurance premium. But then, there are so many factors that feed into those calculations (some companies offer lower rates to women, for example).
My one exception is anywhere where I might be mistaken for a medical doctor (e.g. at the doctor's surgery, dentist's, on flights etc. - though my title is 'Dr' on my credit and debit cards, so sometimes I get 'found out' when booking flights, and I also had it on my US visa when I went over there as I was entering on an academic visa). Mostly booking flights and what-have-you the 'title' field is a drop-down box thing, so using Dr UnheardOf (PhD) is just not an option (and isn't that tautologous anyway... and - dare I say - a bit wankerish-looking - like saying 'In case you didn't notice the first "Dr" I am going to point it out again!'?).
I spent a long time in hospital a few years back. As I have said, I didn't use the title 'Dr', but people who sent cards and things did address them to Dr T. UnheardOf, and invariably they went missing and ended up in the (real) doctors' mail. My consultant thought it was most amusing. Maybe he was just pretending, and behind my back was calling me a wanker, but I don't think so...