Have a look at http://onyxneon.com/books/modern_perl/ This is from the author of the book, there's a nice pdf preview there to show the book off and a way to buy it.
Preview is a slight understatement, it's the full book as both pdf and epub.
It is a bit of a marketing term, though. Not many of the "modern" features are really new to Perl, but basically rather common modules. In the case of Moose, they do change the language use significantly, but mostly it's about showing that Perl can be used beyond small, one-file Unix scripts. And it's been able to do that for quite a while, the Perl 4 days are long gone.
Still, getting some new-found traction is important, and popularizing some great CPAN modules definitely won't hurt.
There's also the Modern Perl Books blog which delights in rooting around the guts of modern perl (and modern perl debates) -- http://www.modernperlbooks.com/ :)
