Is this a newer model Hitachi? Mine is about 4-5 years old and I use the micro-adjuster all the time to set the height of the bit, every time I use my router while it's hanging in the table. It's very precise, I love it, except for the fact that they've designed it to sit right beside where the electrical cord comes out of the body of the machine.
Perhaps you could explain what the problem is? I have my instruction book which might help, I just need some idea of what isn't working for you. Do you have it installed correctly?