The journal platform team here at NPG just rolled out machine readable metadata for the papers we publish in Dublin Core, PRISM (good PRISM, not to be confused with evil PRISM) and Google metadata formats.
No more scraping to automatically get the citation for a paper, it's all in the HEAD:
<meta name="citation_journal_title" content="Nature" />
<meta name="citation_publisher" content="Nature Publishing Group" />
<meta name="citation_authors" content="Paul Schenk, Isamu Matsuyama, Francis Nimmo" />
<meta name="citation_title" content="True polar wander on Europa from global-scale small-circle depressions" />
<meta name="citation_volume" content="453" />
<meta name="citation_issue" content="7193" />
<meta name="citation_firstpage" content="368" />
<meta name="citation_doi" content="doi:10.1038/nature06911" />
Useful for apps like Zotero and Connotea (which before now downloaded two files each time you bookmarked a Nature paper: the page itself and then the linked EndNote file to parse).
The metadata will be there for all papers going forward and back through some of the archives.
For fulltext indexing of papers behind the paywall you can use the linekd OTMI file (I only just saw Twease, which does just that) although there's only OTMI for Nature papers at the moment, I think.
Lastly at some point in the future we're aiming to put XMP metadata in our PDFs, which should make it much easier for scripts and applications (like Papers) to look at PDF files on your filesystem and work out what they represent.