We need some facts about what the Semantic Web can be used for. The SWEO case studies provide a great start, listing deployed corporate Semantic Web applications. I added them up, identifying some key benefits: profit, data integration, querying, and taxonomies.

Read my notes.

At ISWC2005, one talk presented a slide about "what are the key reasons to use Semantic Web". Sadly, I lost the reference and the paper did not list them (do you know which paper this was? It was presented in the industry track).
Interestingly, there is not much data available about the actual benefits of deploying Semantic Web technology. To create such overviews, we can either do interviews and questionnaires or look at documented case studies.

The Semantic Web Education and Outreach SWEO Interest Group of the W3C did collect and publish 27 case studies and 10 use cases (numbers as of 22.4.2008). The case studies report of deployed systems, therefore I concentrate of them. As methodology, I copy/pasted all key benefits into a spreadsheet and mapped them to classifications I made up on the run. I added explanatory text about the categories by copy/pasting statements by the authors. Then I sorted the results, showing the top-named benefits first. One argument from a use case could map to multiple of my categories (i.e. when a benefit touches both a business profit and is about data integration, it will be added to both categories).

Read the whole report with the data.

The correct scientific method to do such study would be to use questionnaires and to check if the statements given by the authors are true, so the scientific value of this note is questionable, but I love controversy.