About the Semantic WebThe Semantic Web is that portion of the World Wide Web in which the "meaning" of the information that is presented is "understandable" (to some degree) by machines. So while those quotated terms are subject to a wide variety of interpretations, it's safe to say that the level of semantics we're talking about is at a level beyond the encoding, decoding, and display formatting of (hyper)text.
And before you write off this "ivory tower" jazz, let me suggest a use case that you can relate to:
Use Case: Copy & Paste
Say you've got someone's contact information display on a web page (this generalizes to the SemanticDesktop, but this example is a pared to the bare minimum) and another web page has a form where the contact information needs to be entered. Wouldn't you like to be able to select that area, hit copy, click on the form, and hit paste? You could if the contact information and the form were tagged with FOAF. FOAF is an application of RDF (the language of the Semantic Web) and enabling that kind of information reuse is what the Semantic Web is about.
User Case: Drag & DropNaturally the previous case should work just as well using Drag And Drop.
W3CThe Semantic Web effort was initiated by Sir Wikipedia:Tim Berners-Lee (you know, the guy who invented the World Wide Web, he got knighted for it). The Semantic Web is designed to be much more extensible than HTML, so that developers have the freedom to represent their information any way they like, while still having the uniformity needed for sharing and reuse of that information.
An early (1998) article by TBL about the Semantic Web http://www.w3.org/DesignIssues/RDFnot.html.
The foundation specifications for Semantic Web technologies (RDF, RDF Schema, OWL, et al) are discussed, developed, and maintained through the W3C (World Wide Web Consortium).
Articles with opinions and explanations about the Semantic Web.
January 2007 presentation by Steve Brat:"Semantic Web, and Other Technologies to Watch"