Jason: "I am very tempted to do something similar for mobile phone numbers!" – Great idea. I get cross-eyed when I scroll through my contact lists on my PC as well as my cellphone.
 Dominic Cronin comments: "Perhaps it also makes sense to use this when managing a network with lots of different machines." – Bingo, Dominic! Using identicons instead of using the same PC icons in the list or graph of machines in the network will make it easier to distinguish them.
Using identicons to represent products (i.e. ISBN or SKU) will enhance readability of invoices, shipping list, etc.

I'll update this post as suggestions keep rolling in. 🙂

Some design tips:

Multiple Types of Identicons in a Page

If your use case uses more than one 'class' of identicons within a single page (i.e. wiki page using identicons for names as well as links) then you can help users distinguish different identicon classes by wrapping them with class-specific borders (i.e. circle for people and square for links).