Is perl 5.8.0 production ready?

I'm not sure what you mean by this question. 5.8.0 is 5.8.0 and will always be 5.8.0. The 5.8.0 in two years is the same 5.8.0 as the one that was released. If it isn't "production ready", it will never be.

Perhaps you mean, "can I use it in production?". See below.

Are there flaws/support issues big enough to make you think twice?

Yes. But they were there with 5.6.x too. There are known bugs and problems with 5.8.0. There are known bugs and problems with 5.6.1 too. And with 5.005_03. With every version of Perl. Whether the problems with 5.8.0 are serious for your production environment, we cannot tell. You will have to use your test environment to find out.

Will I have any module problems?

Maybe, maybe not. Before 5.8.0 came out, people have tried out modules, with particular focus on the most popular CPAN modules. Bugs have been found and fixed. Modules have been patched. But were all problems found? Unlikely.

Is perl 5.8.0 threading enough incentive to switch over?

I don't use threads myself, but from what I here over and over again at the local Perl Mongers meetings is that 5.8.0 threads are better than 5.6.x threads, but they still suck too hard to be very useful. They take up a lot of resources.

Abigail