I personally stopped waiting for RDF to become relevant after years of fighting with impenetrable, mutually incompatible specs (page A refers to draft B which has subsequently mutated or 404ed, etc. and although it's years later nobody has updated anything and all of the examples predate either), and horrible tools — nothing release quality, examples don't validate, bugs unfixed for years in the issue trackers, etc. Vendors promise that everything will be sunshine and rainbows if you buy their commercial offerings but the costs are high enough to make any conceivable benefit dubious, etc.
It seems like the single most useful thing which could happen for adoption would be cleaning that up: a clear use case which isn't already well solved and a good tutorial outlining the benefits with non-trivial examples which follow the current standards, validate and introduce production quality tools. If any of that exists, it's managed to stay completely off the mainstream computing radar, which is a pity given the number of smart people who've poured considerably amounts of time into it.
As an example: a lot of the RDF community hated schema.org when it was announced because it used HTML5 microdata instead. If you were a web developer, the case for microdata was easy: add a couple of simple HTML attributes, use one of multiple high-quality validators to test your markup, and Google/Bing/etc. would return better search results for your data. At the same time, it was daunting to write an RDFa equivalent because there were no complete, current, non-contradictory docs and examples, the W3C validator had been broken for over a year (it was at least up, unlike all of the other online validators) and nothing actually supported it so you'd be investing hours or days instead of minutes in the hope that at some point in the future it would become useful. Most people with jobs to do are just going to wait until the demand side of that equation is more favorable.
The best example of linked data in widespread usage is Facebook's Open Graph markup but it appears that almost everyone simply stops as soon as they get the desired results in Facebook and, predictably, almost none of the examples actually validate because of tooling and cultural issues.