The atmosphere on PerlMonks is definitely nicer, and there is a lot more conversation going on here than on Stack Overflow. The threaded model allows multiple refinements of a solution, from several contributors, to an extent that the single-level answer + comments model of Stack Overflow cannot match.
That said, I like the Stack Overflow interface, it's very well thought out, the message that warns you about answers to a question while you're writing yours for example is really helpful. I just hate the fact that other people routinely edit my posts.
Also I think it is important that Perl has a presence there, as part of our ongoing effort to make the language and its community more visible. It is a real shame that at the time of this writing, the 'perl' tag is less popular than the 'delphi' one, and way less than any other mainstream language. Because whether we like it or not, it is one way people use to assess the popularity of a language, and whether they are willing to use it.