Agreed. The singleton is, when you get right down to it, really just a hack to add global variables to Java in an "object-oriented" way, dignified with a fancy name and notable mainly for being the design pattern people are by far the most likely to be able to remember off the tops of their heads.

There are very few cases where singletons add value in a language like Perl. If your code is worth the effort of moving away from global variables, it's worth the effort of generalising completely (for example, allowing people to have multiple data sets open at once).