There are various ways to measure it, but Danny Ayers shows that where it counts, it's making progress.
A few months ago, Danny Ayers said that he was looking for work. Now, he writes
I seem to have a fairly constant flow of work offers, the majority being frustratingly interesting Semantic Web-related contracts. So if anyone’s actually looking for this kind of thing let me know and I can pass names along.
You can count up your sourceforge projects, or the amount of RDF data or school projects or Technorati mentions or whatever you like, but if someone who specializes in semantic web work is finding too much of it out there, that's a real indicator of progress.