IMHO, Perl is not good if you made some system programming at low level (like Linux Kernel Modules) and if you wonna to minimize memory usage.

I hapilly use Perl for 1), 3), and 4) every day :)
2) can't be made on Linux kernel without patches at all (if you need realtime maybe you need Qnix or RTLinux ?. And as soon as real realtime will be guaranteed by kernel, you will be able to write realtime things in Perl,