So PLS has a post up lamenting the worth of the obligatory committee meetings in graduate school. From my standpoint, they have been helpful to me, but it depends on the individual and the situation. First off my institution mandates that we have these little pow wows every 6 months, starting midway through your second year, as a way to ensure you are working and meeting milestones that are set by primarily your PI and your committee. They also serve as a method to ensure a trainee isn't being abused or treated unfairly as a PI, but this can vary and is typically not the case. The committee meeting also can be a place where a PI can use three to four other people to help get their subtle points (work harder, focus dammit, or watch your grades) to the slower and stupider of my species.
The value of my committee lay in initially stacking the deck with people that are players in my field and serve as great internal reviewers to my proposed experiments. They will ask me controls, why don't I do this instead, or tell me to also consider this because for my paper because the damn reviewers seem to be harping on this lately. Also don't be afraid to change out committee members, as soon as I've gotten all that I can from them (expertise or feedback), its time to jettison them and get a new one. I did this before my last committee meeting, getting rid of a member who sat there and ate my cookies but gave little feedback. And swapped him with a PI who we could generate a collaboration with. I wanted to study the role of my enzyme on a process that he studies in his lab and didn't really know the techniques to do this. Now we are working together.
So from a grad students perspective, I think the mileage on committee meeting worth may vary, but its what you make out of it.