I also have had it drummed into me that breakfast is the most important meal.
In practice, I have found it to be mainly true in that if I eat a good, hearty but low-carb breakfast (omelette, bacon, veges...) not only does it keep me going till lunch with no need to snack but also I find it easier to eat well (ie primal) the rest of the day.
Usually I do actually feel hungry for breakfast about an hour or so after I wake up and have had a couple of cups of tea. Very occasionally I don't feel hungry and just forget to have it.
On the other hand if I were to start the day with toast and jam or cereal and fruit, I would be hungry again and grabbing yet more carbs within a couple of hours at most. So from that point of view I think yes what you have for breakfast is very important, when you have it possibly less so.