So I just let the reps know before I started the nurture that they'd be getting the bounce backs, not sure what (if anything) they do with that info. If we really were looking to clean up bounce-backs (we don't get that many right now) we could prob set up a rule in their Outlook accounts to fwd those along.
For other bounce backs, I usually get them and if someone has changed companies, etc. I mark it in their lead record.