With all due respect to Damian Conway and to his absolutely excellent book (whose recommendations I do follow on a number of items, well, most of them), and I certainly don't claim to challenge his authority, I still have to disagree.
The line length and the tab recommendations are, to say the least, debatable (at least in my view).
I had dinner last Monday with Curtis "Ovid" Poe and brian de foy in Paris (social setting with the Perl Mongers in Paris), and we discussed briefly these matters, my feeling is that both of them agreed that using spaces rather than tabs is not the best idea.
To brian and Curtis: if I misrepresented what you said in any way (I don't think I did, but just in case), sorry about that, I did not mean that.