I agree Andrew...
It would be great to see more:
* Libraries that making the developer life easier.
* Cool demo to what can be done with web workers today and transferrable objects.
My little contribution is with this set of examples (from the book) -
http://greenido.github.com/Web-Workers-Examples-/
As for "Are web workers still too immature/unsupported?"
I would say that our current state is much better and in the near future all the major browsers will have them:
http://caniuse.com/#feat=webworkers
Any comments/ideas to new demos are most welcome!