Does anybody use semantic techniques (RDF, OWL, machine reasoning, etc.) in comercial apps or is it still an academia's toy?
Oracle have done some work and IBM have done some research too.
I studied the semantic web at university a couple of years ago and I wasn't convinced then. It doesn't seem to have made much progress beyond academia since then.
The basic problem is that needs to get a critical mass of ontologies to be widely used, but creating that critical mass is too difficult so it just isn't going to happen.
Some other questions that are related:
There are many organizations who have started using it. Like BBC Programmes and BBC Music, Crunchbase, OpenCalias are few examples. Many Biological data repositories store data using these technologies as well. Commercial software to store and query RDF like virtuoso are also available.
Search engines have also started using and displaying such data (For example see Google snippets)