I love the pet A.I. that really makes pets individual. My first dog was a somewhat playful, very loyal guard dog, then I had a lazy elderly St.Bernard and then I brought a hyperactive and curious stray from Selvadorada. That dog was something, constantly raising himself up at any counter he could find and zipping through the house at a speed I hadn't know possible!
My favorite pet moment is getting Mowgli from one save to another. I was playing a side save in which my Phillips family adopted a cat, said Mowgli. After finishing the side save, I wanted to bring Mowgli over the main save. I saved him to my library in the throaway save and then pulled him out again in the main save.
Now Mowgli's most distinct quirk was to eat human food whenever it was left unattended for a micro-second. But after getting imported, he didn't want any. I tried Maxis food and cc, stuff he'd had before and new things, to no avail. Finally I forced Mowgli to eat with ControlPets, but he wouldn't do it on his own anymore.
Then, a couple of ingame weeks later, I visited the Phillips family with another sim. Now guess the sight my visitor was greeted with: Mowgli on the kitchen counter, going at leftovers with abandon. Finally he was feeling at home :) and ever since he's back to his old self.