I have seen at least one of almost all of the new pets. I haven't seen a single book or infinite whelpling, and I haven't looked for the two new ones in Pandaria yet. I have looked for all the others and found at least one...most of the time...exactly 1, over many...many hours spent checking. The only pets I found multiples of when I went looking was the harpies and the yetis. I searched most of yesterday and for several hours this morning on VERY low pop servers (where there is often a minfernal or two running around) with basically no luck. This leads me to believe that on a scale of 1-10, with 7 being MF and SW, ALL of the new pets fall somewhere between a 6-10 in rarity, with many of them being FAR more rare than SW or MF (due mostly to the fact that the area they can spawn in is super tiny). So now instead of having 2 super duper rare pets, blizz has kindly given us 13 new ones.
Isn't it fun to stare at your screen and do nothing for hours at a time just so that when that 1 pet spawns you can be there to find out it's a poor? I know I love the new "exciting pet battling action" that is taking place thanks to all these new pets!
EDIT: So I just read this on MMO champion. It's a blue post...
Patch 5.1 New Pets
The new pets are on fairly long spawn timers, and are randomized (i.e. will not spawn on server restart). We've confirmed they have been spawning on some realms, so just keep an eye out!
Is "some" realms rather than all the realms working as intended? Which special realms are these so I can go make alts on them?
They're random, so they're not going to spawn on every realm at the same time. So yeah, working as intended.
So it seems that they are only spawning VERY rarely with REALLY long spawn timers on SOME realms and not on others! HOLY CRAP! If this means what I think it means, I rescind what I said above and will, without a doubt, say they are all 10s on the rarity scale listed above making them WAY more rare than SW or MF...holy crap!