It's pretty well accepted that Perl 6 is at least another year away, and for widespread use I would expect it to be 2 or 3 years away (think about all the modules that will probably need porting). That's a long time to wait for a new programming language to be widely usable. I'm not suggesting that Perl 6 isn't going to be chock full of good ideas, but it's not here yet, and until it is a regular day-to-day coder simply can't consider it as an alternative option.
Secondly, yes Perl 5.8 supports pretty stable threads, but there are still some major issues with them, for example creating a thread under iThreads is several orders of magnitude slower than forking a separate process. For other issues follow the perl5-porters mailing list, or grep the archives for Elizabeth Mattijsen's posts.
POE however is here, it works, and it does what its supposed to do really really well.