The Semantic Web is a Web of Data — of dates and titles and part numbers and chemical properties and any other data one might conceive of. The collection of Semantic Web technologies (RDF, OWL, SKOS, SPARQL, etc.) provides an environment where application can query that data, draw inferences using vocabularies, etc.
However, to make the Web of Data a reality, it is important to have the huge amount of data on the Web available in a standard format, reachable and manageable by Semantic Web tools. Furthermore, not only does the Semantic Web need access to data, but relationships among data should be made available, too, to create a Web of Data (as opposed to a sheer collection of datasets). This collection of interrelated datasets on the Web can also be referred to as Linked Data.
To achieve and create Linked Data, technologies should be available for a common format (RDF), to make either conversion or on-the-fly access to existing databases (relational, XML, HTML, etc). It is also important to be able to setup query endpoints to access that data more conveniently. W3C provides a palette of technologies (RDF, GRDDL, POWDER, RDFa, the upcoming R2RML, RIF, SPARQL) to get access to the data.
Linked Data lies at the heart of what Semantic Web is all about: large scale integration of, and reasoning on, data on the Web. Almost all applications listed in, say collection of Semantic Web Case Studies and Use Cases are essentially based on the accessibility of, and integration of Linked Data at various level of complexities.
A typical case of a large Linked Dataset is DBPedia, which, essentially, makes the content of Wikipedia available in RDF. The importance of DBPedia is not only that it includes Wikipedia data, but also that it incorporates links to other datasets on the Web, e.g., to Geonames. By providing those extra links (in terms of RDF triples) applications may exploit the extra (and possibly more precise) knowledge from other datasets when developing an application; by virtue of integrating facts from several datasets, the application may provide a much better user experience.
Tim Berners-Lee's note on Linked Data gives a succinct description of the Linked Data principles. The Semantic Web community also maintains a list of books on a W3C Wiki page. Some of those books are introductory in nature while others are conference proceedings or textbook that address more advanced topics. Details of recent and upcoming Semantic Web related talks, given by the W3C Staff, the staff of the W3C Offices, and members of the W3C Working Groups are available separately; the slides are usually publicly available. The W3C also maintains a collection of Semantic Web Case Studies and Use Cases that show how Semantic Web technologies, including Linked Data, are used in practice.