Here's my dilemma: Most MSD's I've seen know the title is a joke. I've seen some excellent MSD programs put together and think that title is fairly accurate, but that doesn't seem to be the norm in my neck of the woods.
On the other hand, I'm proud of my Master Instructor rating. To be honest, I thought I was going to stop at IDC Staff, but after the umpteenth OW student asked me if I was working on becoming a divemaster someday, I realized that title DOES mean something to some people. So I went for Master Instructor. New students immediately realized I was the high man on the totem pole amongst the staff (which was good because I was younger than most of my students). I will vehemently defend my ranking and my training because I KNOW I was trained by one of the best facilities on my side of the country and I have the certifications, lack of QA investigations and happy student testimonials to back it up. But I've seen other MI's that I wouldn't allow to assist with a class.
So I see a purpose in the title, but I also see that ultimately it comes down to the training behind the title.
(As an MI, I've tried to join on with new shops when I've moved and ALWAYS get the speech about how "we train to a higher standard than most", yet when I get in the water with them, there are standards violations right and left. So even having a title and coming from a well known, respected program doesn't really get you anywhere.)