Actually, I don't think Amazon or anyone makes much use of the internal metadata. It seems one always has to provide it externally as well when the book is uploaded.
That said, I think it's a good idea to provide as much metadata as possible just so it's there.
We first build the epub, add metadata, and convert epub to mobi using kindlegen. I don't know whether all of the metadata makes it into the mobi or not. According to Calibre's ebook-meta program, some doesn't.
Here are examples of the sort of dc metadata we use:
Code:
<dc:title>The Mudslinger Sanction</dc:title>
<dc:creator opf:role="aut" opf:file-as="Mills, Gerald">Gerald Mills</dc:creator>
<dc:subject>psychokinesis, scientists, suspense</dc:subject>
<dc:publisher>Twilight Times Books</dc:publisher>
<dc:identifier id="BookID" opf:scheme="urn:isbn">9781931201704</dc:identifier>
<dc:language>en-US</dc:language>
<dc:rights>Copyright © 2002 by Gerald Mills. All rights reserved.</dc:rights>
<dc:contributor opf:role="edt" opf:file-as="Quillen, Lida E.">Lida E. Quillen</dc:contributor>
<dc:contributor opf:role="art" opf:file-as="Ozinga, Kurt">Kurt Ozinga</dc:contributor>
<dc:coverage>U.S., 20th Century</dc:coverage>
<dc:date opf:event="issued">2006-04-15</dc:date>
<dc:description>When Dr. Gordon Whittier is kidnapped for bait, Jim sets out to rescue him against all odds. His powers are pitted against ruthless murderers, a brilliant computer hacker, the FBI's best, and the clock in a race to save Whittier's life. All he has to work with is a trail of clues and his talents, but to succeed he must learn to use his force against theirs.</dc:description>
HTH