I've used it too, and it definitely boosted my supply when I took it consistently. Check out this info sheet about Domperidone that my LC emailed me. And also Dr Jack Newman's site for more info.
Here is another snippet of info from his site that might be useful:
"How long does it take for domperidone to work?
It depends on the situation. In a situation where the mother had had a good milk supply, but it decreased for some reason (e.g. going on the birth control pill), domperidone often works very rapidly to increase the milk supply. Often, within a day or two the mother is seeing a difference (and so does her baby). But this is not always so, and in many situations, it may take a week or more for the mother to start getting an effect. On occasion, we have had mothers only starting to get an increase in their milk supplies a month or more after starting to take it. Therefore, we generally recommended that the mother take the domperidone for at least six weeks in order to be sure whether it has worked or not."