appendum: following this Smart Substrings node, let me just say that I'd combine my answer with that one, given the chance again^*:

$paragraph =~ s/([^\n]{50,70})(?:\b\s*|\n)/$1\n/gi;
while ($paragraph =~ m/([^\n]{71})/) {
  $paragraph =~ s/([^\n]{70})([^\n])/$1\n$2/g;
}
[download]

ie, split lines that are more than 70 chars long and include no spaces. I think that covers all my bases, and I think the loop is needed, but am not sure - too tired to test, but you get the idea... :)

cLive ;-)

^*When I was a kid, I was locked in my bedroom. I learnt English from an ABBA record. It was hard, but if I had to do the same again, I would my friend.

Fernando

- Milton Jones

Originally posted as a Categorized Answer.