It's very difficult to decide what is off-topic with Perl. In many uses it's a glue language, it sticks things together. A conversation about glue without discussing what it's sticking is very difficult, and more than a little limiting. I'd personally say off-topic is where it begins to veer violently away from Perl.

Easy to say this, but harder to handle. I'd say a Unix tutorial on how to use the command-line to use Vi or Emacs* to edit a Perl script, and then get round a few common problems such as file permissions, and the Perl bangpath to actually get a working program would be fine, whilst a Unix tutorial on how to do firewalling on the Linux 2.4 series kernal would be OT.

An indepth look to internal communications such as sockets, pipes, and signals, their pros and cons, and Perl snippets showing use would be exactly on-target. The same without the Perl examples and how it factors in much less so.

I'd even like to see an article where it shows when to stop using Perl and go to another tool. When to switch your CPU-heavy code to C and link that with your Perl, when to rely on the Unix command tools, and when the task isn't suitable and maybe you should jump ship altogether. I know that last bit is likely to get me beaten up in dark alleys by stealthy Perlmonks but the truth is every tool has that limit. Of course you can stick Perl to the new tool though..

Essentially the question I suppose is "Is this Perl, Can I do this with Perl, will this directly aid my Perl?". If the answer is Yes then it's probably not off topic. If the answer is No then try to introduce that bit more Perl content.

(*- Delete according to religious affiliation)