You care about your identity and your tweets on Twitter. So, this is a sensitive account. It wasn't clear earlier whether you cared about your perlmonks.org identity so much. So, assuming the worst case scenario, this should have been considered a sensitive account as well.

This means that ideally you should have chosen two different passwords for both these accounts.

For some sites like reddit, HN, etc. one may know very well in advance that they don't care about their identity and they would be happy to create a new account when they lose one. I think these are the only cases where password reuse is justified.