In response to the ReadWriteWeb piece titled: Semantic Web: What is the Killer App. by Alex Iskold:

Information overload and Data Portability are two of the most pressing and imminent challenges affecting every individual connected to the global village exposed by the Internet and World Wide Web. I wrote an earlier post titled: Why We Need Linked Data that shed light on frequently overlooked realities about the Document Web.

The real Killer application of the Semantic Web (imho) is Linked Data (or Hyperdata), just as the killer application of the Document Web was Linked Documents (Hyperlinks). Linked Data enables human users (indirectly) and software agents (directly in response to human instruction) to traverse Web Data Spaces (Linked Data enclaves within the Giant Global Graph).

Semantic Web applications (conduits between humans and agents) that take advantage of Linked Data include:

DBpedia - General Knowledge sourced from Wikipedia and a host of other Linked Data Spaces.

Various Linked Data Browsers: Zitgist Data Viewer, OpenLink RDF Browser, DISCO Browser, and TimBL's Tabulator.

zLknks - Linked Data Lookup technology for Web Content Publishing systems (note: more to come on this in a future post).

OpenLink Data Spaces - a solution for Data Portability via a Linked Data Junction Box for Web 1.0 ((X)HTML Document Webs), 2.0 (XML Web Services based Content Publishing, Content Syndication, and Aggregation), and 3.0 (Linked Data) Data Spaces. Thus, via my URI (when viewed through a Linked Data Browser/Viewer) you can traverse my Data Space (i.e my Linked Data Graph) generated by the following activities:

Blog Posts publishing
My RSS & Atom Content Subscriptions (what used to be called a "Blogroll")
My Bookmarks (from my Desktop and
and other things I choose to share with the public via the Web

Virtuoso - a Universal Server Platform that includes RDF Data Management, RDFization Middleware, SQL-RDF Mapping, RDF Linked Data Deployment, alongside a hybrid/multi-model, virtual/federated data service in a single product offering.

BTW - There is a Linked Data Workshop at this years World Wide Web conference. Also note the Healthcare & Life Science Workshop which is a related Linked Data technology and Semantic Web best practices realm.