Nice write-up, stevieb, thank you.
I've seen a number of projects using coveralls.io but wasn't really sure what it gives us that Devel::Cover and cpancover don't already. Clearly cpancover only runs on dists published to CPAN, so coveralls.io gives data before publishing which might be useful, I suppose. But the keen author would already use Devel::Cover locally so I'm not really sure of the benefit of using coveralls.io for Perl projects. Could you explain a little about what the advantages are?