Is it worth learning Raku (previously known as Perl 6)?

How could learning Perl be BAD for you? Is there any cost you have to weigh against the benefit of learning (OK there is are the obvious ones of time and money, but if those aren't too bad, what else could there be to hold you back)? IMO, learning things is ALWAYS good. ;)

This has been answered, but I'll step in:

Rakudo Perl 6 is the de-facto implemention of Perl 6 right now. It has the most features, the biggest community and an impressive rate of development. The first "1.0" release, Rakudo Star, is planned for April 2010.

Perl 6 also runs on Parrot, which is a virtual machine already capable of running another couple dozen languages, including Python. The scope for multiple languages interacting and calling each other's modules/APIs is pretty huge.

Even if you don't plan on using Perl 6, the scope of the language is so broad, and contains so many new or borrowed-but-not-yet-mainstream paradigms, that it will have an undeniably huge effect on other scripting languages. It's worth becoming familiar with it for that reason alone.

If I had a training opportunity like this, I'd take it. Even if it was COBOL.

I look at training opportunities as not only an opportunity to learn the highlight technology, but as an opportunity to learn new ideas, concepts, platforms, language (just to see how something else was implemented) and finally, to meet new people.

I think that any training is likely worth my time. Especially if the cost is going to be covered. In a training class, you'll often learn (or relearn) material that could be applied in your language of choice.

Note: It's probably worth me noting that I take a very academic look at software development and programming languages.

If you want to use any version of Perl, then Perl 5 is the way to go. I don't think anyone is using it outside of experimentation. However, Perl 6 and its Parrot VM have a lot of potential as part of a "fourth way" platform for dynamic languages between the current choices of "run it in its own VM," "run it on the JVM" and "run it on the .NET CLR."

A lot of the cleanup work on Perl 5 is being done to make Perl 6 less of a culture shock so it shouldn't hurt you if learning Perl is a goal.