Is there a production-grade implementation available yet? If so, who is using it, and what are they using it for?
I look into Perl 6 every few years, but there's never a high-quality implementation of it. The ones that do exist end up being esoteric, experimental, or otherwise not really usable like Perl 5 is.
Is there a production-grade implementation available yet?
Depends on your use case: There are two reasonably complete and stable Perl6 implementations - Rakudo on Parrot and Niecza on .NET/Mono.
What needs to be addressed before Perl6 can be recommended for arbitrary production use are modules and performance:
The module ecosystem[1] is somewhat ad-hoc and modules may have bit-rotten, so batteries are not included.
Rakudo is more feature-complete, but performance is less-than-awesome and Niecza might be a better choice if that's relevant and you're comfortable with the CLR. The performance issue can be somewhat mitigated by implementing critical code in C (in case of Rakudo) or C# (in case of Niecza), but that's more of a band-aid than a real solution.
You might also want to take a look at the Perl6 advent calendar[2] to gain some insights into the current state of Perl6.
Not that I'm aware of. Rule of thumb from my totally unscientific personal observations would be that the Rakudo of today is at least one, perhaps even two orders of magnitude slower than the others...
I look into Perl 6 every few years, but there's never a high-quality implementation of it. The ones that do exist end up being esoteric, experimental, or otherwise not really usable like Perl 5 is.