I was checking my domain deciding what domains to renew. I usually also check the other extensions in order to make a decision. When deciding to renew or not a .info domain I noticed that the .net had an registrant email address that used the .biz version. Te only problem was that the .biz was not registered at that time.
I tried to warn the domain name owner (by sending an email that went, surprise, unanswered) that not only he had let the .biz expire and he was risking losing the .net either by missing a renewal notice or if a thief used the .biz to create the .net registrant email address and steal the domain. A couple of days later I noticed that someone bought the .biz and is now parking it.
In fact ICANN’s GNSO is suggesting as a best practice in the Expired Registration Recovery Policy that registrars should advise registered name holders to provide a secondary email point of contact that is not associated with the domain name itself so that in case of expiration, reminders can be delivered to this secondary email point of contact.
So it is always a good idea to keep your whois details current and especially to keep your admin/owner email address domain name registered and renewed. I renew my admin email domains well in advance, usually for 5-10 years. It is good practice to also renew any nameserver domains you may have as well.