It's true that longtime HAL cruisers like fixed seating times. It's our preference, too. We are confirmed for 8:30 dining (our choice), but on an Alaska cruise. We booked several months ago for August 2008, and when a family member booked the same cruise a few days later, neither the late nor early seatings were available.
One of the reasons we prefer the set times is that it makes it easier on our son. The waiter gets to know him, quickly learns some of his favorite foods, and surprises him with some of them during the meal. Our guy loves the attention, and as it is his vacation, too, it makes him feel special.
I can see how this option might work on large ships where there is a greater variety of dining choices, yet I'm not so sure about HAL's S-class ships. I'll let you all know in August.