This was going to be a comment on Schwern's post, but it grew.
I would say that moose is slower than "normal" Perl OO, but firstly this is not terribly important for most code (premature optimisation) and secondly if you do __PACKAGE__->make_immutable
then a lot of the runtime overhead is removed anyway.
I'm with the "learn Moose first" gang. I like to remain willfully ignorant of Perl OO details for the kind of code that I write (data management and simple apps), and so I tend to use Moose for everything, even stuff I would have done procedurally in the past, because it makes a lot of the mechanics of the programming much easier