The great thing about petnames is they resemble the way you remember people in real life. You can have your mom recorded as "Mom" in your contact list, and if you want to ask your Mom what Uncle Bob's contact info is, she can tell you... Mom => Uncle Bob. Petnames can also absorb central naming systems: we don't need to throw out dns, make dns a petname then dns => dustycloud.org
It's also less vulnerable to phishing.