Perl is in a state of rapid development at the moment. 2010 was a good year, with the introduction of regular perl core release cycles starting with 5.12.0; Moose reaching 1.00; the release of Rakudo Star, the first early-adopter Perl 6 implementation; and the publication of Modern Perl by chromatic documenting many of Perl's newest features.
What new Perl feature in 2010 do you find most useful?
What is so great about that feature and why do you like it? What does it do and why is that great?
How has it changed the way you code? What specific situations does it improve for you and how does it make your life easier?