What's the migration path for people using perl 5.8.x +?

Perl 5.12.2 will be out soon, and Perl 5.14 comes out next spring.

... is Rakudo ready for work and to take on a heavy load in my job or is this largely still early beta and intellectual in nature?

That depends on the nature of your work.

Where is the documentation?

Perl 6 Synopses and the Using Perl 6 (book in progress) are good places to start.

What do I get from this language that I don't get from perl 5 that would make me want to migrate?

Better consistency, better defaults, and built-in language features that are (if even possible in Perl 5) syntax extensions.