As a % they are dropping.
For instance, those that start with "A" as of 20 minutes ago:
2372 available out of the 17,000 originally available, right around 15% left.
(Less than what's left in less desirable letters, of course).
Running them now through EDTK, there are still some that have decent overture rankings and certainly plenty that I could imagine meaning for.
But with over 200,000 possible combos, it's certainly a case-by-case basis for the domain names, not some blanket statement that can be applied.
-Allan