I've never used formats, threads, XS or XML in my Perl code. XML is of course not a Perl resource, it's just a very verbose way of doing in-band data markup. For formatting output, I've never felt the need of anything more fancy than (s)printf. As for XS, well, if I want to program in C, I program in C, not in XS. And threads, well, I've never seen a reason to use them. To me, there's no benefit of threads over fork/shared memory/4-arg select.

I think that will be interesting to know what resource is not used very much, or what the monk haven't learned yet. Soo, this resources can be reworked, or better docs can be writed.

That sounds you are under the impression everything in your list has to be used a lot, or else there's something wrong with it. If it turns out that only one in 20 people use format, does that mean you feel the urge to stimulate the use of format by "reworking the resource" (whatever that means), or by writing better docs for it?

Say you had a someone different list, with both the .. and ... operators in them, and it turned out that the former was used much more than the latter, are you going to actively promote the use of ... by writing better docs (perldotdotdottut.pod), starting an advertisement campaign (add three inches to your penis by using dot dot dot!) or reworking it such that your computer says "Thank you!" each time you use ...?

I'm a bit of a loss of what you are trying to archieve.

Abigail