Yes, "Perl/site/lib" is a good place to put your module. Make yourself a private namespace so it is unlikely to interfere with future or existing modules or get clobbered by installing other modules.
in reply to Adding user-defined modules under ActiveState
A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James
My blog: Imperial Deltronics