Here's an example from my experience. I wrote a perl script to do something via Telnet, and wanted to hide the password input. I downloaded Term::ReadKey which worked fine, but I had to go round every PC in the department installing the module on each one.
in reply to Re^2: Perl 5's greatest limitation is...?
in thread Perl 5's greatest limitation is...?
When I moved on to a new project, I took the script with me and found a use for much the same functionality, but Term::ReadKey would not install. It turns out that it needs a C compiler.
It's not exactly a weakness with the language, but if we were using C (admittedly with non-standard platform-specific extensions), I wouldn't have needed anything else as I would have hand-coded it pretty easily. In fact a hidden input routine was one of my personal library of C functions back in those days.