I haven't read all the replies, so this may have been addressed already, but...
The concept of getting in for free on your birthday seems like it would only appeal to one day visitors...or two day visitors. Mostly locals, who may like the idea of taking a day off work on their birthday and spending it at the Magic Kingdom for free. But for people who are coming from far away for a vacation, what kind of savings does this really mean? Very minimal.
For example, let's say that my wife and I decided to go in the spring, in late March, and we will be there for her birthday on March 24. If we are staying for 8 days, then she will just have to buy a 7 day ticket, since she will get in free on her birthday. But if she didn't get in free, and she got an 8 day ticket instead, how much extra would she be spending? I honestly can't remember because I don't know right off hand how much tickets cost, or what the per day amount is for those tickets. But I do know that the difference between a 7 day and an 8 day ticket is probably not much more than 10 bucks.
So as a birthday present, we will save around 10 bucks. Whoop dee dee.
I know, 10 bucks is 10 bucks and a penny saved is a penny earned and all that. And I certainly won't complain about saving 10 bucks while I can. But on the other hand, it's hardly worth getting excited about either.