That is a poor example unless Number::Format has improved since I had to debug a co-worker's use of it. Which it probably has. For one thing I submitted patches for the more egregious problems.

What did I dislike, you ask? Suffice it to say that the bugs that I found in that module taught me things I didn't want to know about Perl. Such as that $_ is always in package main (so using its formatting statements in a map statement messed up the passed in array), and my $foo = "bar" if $cond; has some really strange behavior.

It is hopefully much better now. But the scars would still cause me to shy away.