Interesting thread, admittedly I've only skim read a lot of it but here's my 2 pence.
I totally agree there should be just one title for women just as there is for men, be that Ms or whatever. Although tbh it's not the title on a form etc that grates with me, it's when someone addresses me as 'miss'. It sounds like something you would say to a vaguely naughty child, just one step away from 'young lady'. I know most of the time this is not the intention but I find it particularly irritating if it is in a situation that involves exchange of money for example, such as in a taxi or hotel. There is the French 'mademoiselle' that I also dislike. I think as a woman in my mid-twenties I'm allowed to graduate to madame, so to speak. I guess that's the title the French woman is referring to?
Having said that, I don't think 'miss' is on the same level of condescension as the 'Hi girl' I used to hear when I lived in Amsterdam! (this was only a year ago and I do not look THAT young, although admittedly probably the same height as the average Dutch ten-year-old...)
I have discussed this with friends before and a lot have said they prefer Miss as it sounds younger and keeps their marital status a mystery, so I guess it's all horses for courses.
In my culture, though, getting older equals increasing levels of respect and so is considered a positive thing iyswim. So perhaps I'm seeing it through a different lens?
I vote Ms, anyway. Then it's up to the woman to disclose whether she's married or not, in the same way as it currently is for a man.