It's always been my personal policy to log out from a battle if there's a blue pet that I already have (the blue of), but the last couple of times I've done that, the whole team has despawned. It's a bit crappy if you can't even be nice and leave a rare that you already have for someone else. I thou...

When the Pet Journal first appeared pre-MoP, I had 1170 pets... I love all my toons equally so of course I had to get as many pets as I possibly could for each of them! And I'm such a hoarder (and a cheap one at that), that I couldn't bear to just dump any that could be sold or given away to friends...