My rule of thumb is a bit different: when on Windows, upgrade to Linux.</tongue-in-cheek>

Ok, not really. (Well, not entirely anyway...) My rule of thumb is to use perl anyway, just because then portability is an easier goal. And it should (generally) be a goal, even if it's not required yet. Exceptions obviously apply (e.g., if the program is only supposed to interact with very OS-specific situations, though those should be fairly rare, I'd hope). Why learn multiple toolkits when you can learn a good multi-purpose toolkit deeper? My big project at $work where I basically started with Perl works on Windows, Linux, AIX, Sun, and, as of fairly recently, Mac OS X (with almost no changes) (heck, for the most part, I can run the application on Linux and tell it to pretend I'm on Sun or Windows, and it still works properly). I find I can be more productive by keeping focused on good all-purpose, cross-platform languages than delving into monoculture (no pun intended) languages.