The most important thing to comment are the assumptions you (the programmer) made. For example, "$var must not be undef.", "This algorithm is only ideal for lists no bigger than XXX elements.", "The module may not be thread-safe." and "Uses features specific to Win32."
I understand that you were merely making stuff up off the cuff, but I think those are bad examples. Any assumptions should really be coded as assertions and the comments should explain why the check is there. 
#sub foo() which sets $var can never fail for such and such reason
defined($var) or die "\$var must not be undef.\n" 

#I'm too lazy to make it work properly for all lists
(@list > $XXX) or warn "This algorithm is only ideal for lists no".
                       " bigger than $XXX elements." 

#cross platform compatibility is comming in version 9.0
($^O eq 'MSWin32') or die "Platform not supported"

[download]
...etc.

In reply to Re^2: Meaning of Maintanability and Functionality in Coding Perl by Anonymous Monk
in thread Meaning of Maintanability and Functionality in Coding Perl by neversaint

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