Dan Brickley posted a great entry on the FOAF weblog on Identifying things in FOAF. I think this might be one of the most down-to-earth illustrations of the Semantic Web I have read.

Marc Canter and Danny Ayers each added some good comments to Dan's post. I added a comment in response to their's, which actually describes the 3-4 basic system/tool ideas of the iCite net:

1. another level of DNS-like mapping to specific documents that gives those documents non-volitile identifiers
2. document stores that automatically plug-in to that DNS-like mapping, and provide interfaces exposing the stored documents to queries
3. tools for querying, caching, and syncing document data across different document stores
4. (safe and easy to integrate with existing/other tools, like websites, blogs, wikis, and email, and with other standards like N/echo and RSS!)

I should add that the iCNS + iCite Container system automatically creates non-volitile identifiers at the item level, akin to PurpleNumbers. So, technically, the DNS-like mapping extends down to the paragraph/block level.

(Thanks to Danny for posting the link to Dan's post, which I somehow otherwise missed).