The main motivation behind state variables in perl5 land was to get rid of the awful hack:

my $var if 0;

Which was a way of getting state variables, but worked on an undocumented side-effect of how lexical pads are implemented. And the code is neater than having to close a an external variable over a routine.

The main patch (although there were a few tweaks a couple of months later as kinks were ironed out), as landed in the repository, is quite small, all things considered.

Basically it's just a tweak on lexical variables.

Another nifty feature of 5.9.4 is that $_ can be made lexical.