Well, I can tell you what's the use of learning Perl 5 and that I suspect most of it will apply to Perl 6 as well:

Perl, more than any other language I know, sacrifices nearly every other property in the name of being useful. It's not a conceptually clean language, or an elegant one, or a simple one, but if you need to get stuff done, now, there is very little that can compete with it. (At least for some rather specific values of "stuff" - Perl, IMHO, really shines at small-ish scripts that need to convert data from some format to another, or merge data from different sources, especialy when lots of text-handling are involved). Parsing a log file, or matching user accounts from a Windows domain with employee records in an ERP system's database are two examples that come to mind because I had to do those things not too long ago.)

Perl 5 has problems though, especially when it comes to writing large-ish programs. While you can write readable und unreadable code in any language, Perl makes writing unreadable, unmaintainable code easier than, say, Python. Perl 6 tries to fix a lot of this while remaining as useful as Perl 5 (or at least trying to).