• The quality and the tone of the answers are better than SO.
• Good, interesting questions typically get a good answer in an hour. (I've been stuck a few times with a deadline, and PM saved my bacon.)
• A really good question gets someone generating alternatives and benchmarks and best-in-class solutions.
• Anyone can ask or answer a question on PM, immediately, even anonymously.
• Anyone can vote on answers on PM immediately (although there is a daily vote limit, for everyone, based on XP).
• Search engines still put PM nodes at the top of the results, so I still go to PM, even when I didn't find my result in PM's own search. And I assume those nodes are some of the best answers to my queries.

Questions on SO are likely to be seen by more people, and have some probability of being higher quality (or at least, more variation). But the hurdles to a good experience on SO are too high for me. I have accounts on various forums there, and since I don't try to be an Answer Firstie, and I'm mainly looking for my own answers, it takes a long time to get enough reputation to be allowed to fully interact.

The fact that I have to have more reputation points to comment, than to actually answer, is backwards. In some cases I would create an answer that was really just a comment, polluting the usefulness of that question.

To take a page from SO, it might be useful to be able to mark a response as (an/the) "accepted answer", or maybe even more than one. But this also causes some confusion, as the first decent answer might get nominated, and the rest ignored. It might be better to see, on responses to your own question, what the votes are, without voting on them first. This is likely to hit newbies and verbose question writers. But probably not a big deal (just "read the answers, try them out, and make your own decision" works better for those with a little patience.)

I keep coming back to PM because people here ask interesting questions, give interesting answers (which are sometimes not expected based on the question), and are generally helpful to all levels of experience. (Yes, there have been a handful of people who have rubbed nearly everyone the wrong way. But they can still post.) I keep coming back because, while I'm not actively coding in Perl in my $work, I still use it, don't want to forget it, and hope to get paid for it again some day. (I really need to get on with Perl 6. It's too much fun to just watch from the bleachers.)

I keep coming back to PM because I feel like I know (some of) the people here, and they're old friends. It's a community with a purpose. SO feels like a truckstop on the interstate -- it feels like no one cares who you are, or if you'll be back tomorrow or next week.