You will find this thread interesting: I have been away from perl for a long time. Need suggestions for getting back in the game!.

(Update: the thread above also mentions Dominus' book "Higher Order Perl". It is now available for free download, and I very much recommend it).

As for the most useful perl-5.10.0 features I especially like say (like print, only shorter, and adds a newline at the end) and the // operator, which is like || except that it tests for definedness rather than truthness.