Linked Data - link instance data, not just metadata
One clarification I forgot to emphasize clearly enough in my recent post on Linked Data is that the real goal of Linked Data is for a given Semantic Web application to link to instance data of other Semantic Web applications, not merely to reuse existing metadata. The goal is to aid discovery of other things by users (and their agents). Reuse of metadata such as vocabularies and schemas is a really good idea, but not sufficient to connect things into a Semantic Web.
An unfortunate side effect of using the single concept of a URI to refer to both data and metadata is that the emphasis on linking gets diffused onto both usages.
In summary, reuse of existing vocabularies and other metadata from other Semantic Web applications is good, but linking to instance data from other Semantic Web applications is what Linked Data is really trying to get at.