Here's a very nice explanation of the Law of Demeter.
In thinking about this and its relation with Domain Driven Design makes me think of something that initially seems like a good guideline. You should watch very carefully for "Demeter" violations between aggregates, but within an aggregate they are probably less dangerous.
Focusing on custom messages between your aggregates in DDD would seem to be a big help in two ways. First by helping root out your aggregate boundaries during design, by looking for high level behavior conversations that might exist. Second by helping to break data dependencies between aggregates that might otherwise be very tempting to introduce when trying to persist that group of objects.
I think paying more attention to obeying the Law of Demeter between aggregates and worrying about it less within the group might be a good way of keeping balance between creating custom messages for everything and re-using data attributes inappropriate in a way that makes code fragile.
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