I think it's a pretty good bet that most Perl authors shop their book proposals to O'Reilly first. I know I did. It's not just that we're all O'Reilly fan-boys, they're simply likely to sell more copies if everything else is equal.

In my experience with Writing Perl Modules for CPAN, O'Reilly wasn't willing to take a chance on a "community" (read underperforming) title. APress was. So I'm an APress author.

I think there's plenty of room for more than one publisher of Perl books. Sure, there will be some duplication of effort ("Beginning Perl" versus "Learning Perl" for example). But there will also be more room for "community" books with multiple publishers, which is nice if you're in the mood to donate one.

-sam