From now on, DOIs, expressed as HTTP URIs, can be used with content-negotiation.

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We expect that that this development will round-out CrossRef's efforts to support standard APIs including OpenURL and OAI_PMH and we look forward to seeing DOIs increasingly used in linked data applications.

This is very cool... content negotiation against 46 million CrossRef DOIs, returning a number of formats including RDF/XML. I would expect this to put DOIs firmly at the heart of any future Linked Data activity in the scholarly space.