The first bit of collecting occurred when I received a Tweet about a certain little cow. Thanks to @JiangWing I was quickly a happy owner of the Pygmy Cow.
You can collect this pet once you've upgraded you garrison Barn to level 3. A special mug will spawn on either the first or second floor, and looting it will yield the pet.
I found mine on the second floor, but there was no obvious way up. You need to use some creative mechanics; the engineering goblin glider comes to mind. But I'm no engineer so I used Wing's recommendation and built a level 2 Gnomish Gearworks. The main thing I was looking for with the gearworks was the XD-57 "Bullseye" Guided Rocket Kit. The item you can loot from this plot changes each day, so I was lucky that the rocket spawned that particular day!
Using the rocket, I managed to get up onto the second floor and collected my adorable little cow. The mug that you're looking for doesn't have any type of glow or indication that it can be looted, until you hover over it with your cursor. As mentioned before, it can spawn on the first floor as well. Usually among the other mug props, so I would be sure to check each one of those if you can't find it on the second floor.
I finally got around to collecting the different spore pets of Draenor. There are currently only three available, two of which required some time to find.
The first one is a drop from a rarespawn named Rotcap. It's a straight forward find, and there's already a Wowhead map to help you find him. :P Rotcap drops the Brilliant Spore.
The second and third spore pets were a bit harder to collect. They require some jumping around and can be obtained by looting spore-like objects found in their respective zones.
Crimson Spore comes from a Strange Spore in Gorgrond. A map to indicate where to look doesn't exist yet, so I had to go by descriptions detailed by other players. Here's the location of the spore on the map:
(click image to enlarge)
You'll find protruding red fungus things on the side of the cliff. The Strange Spore can be found on one of those "fungus stairs", and is fairly easy to get to. Jumping around is your friend. :)
The last spore, Umbrafen Spore, was the hardest to find and reach. It's located in Shadowmoon Valley, and can also be looted from a Strange Spore. Head to Elodor, and follow the road all the way up the mountain. Climb as far as you can up the mountain located north-west of Elodor, and then jump down to the largest mushroom nearby. Here's a map so you can see which mushroom I'm talking about:
(click image to enlarge)
It took me a few tries to actually find it, but the jumping portion was easy. This spore was tricky because I couldn't actually see the lootable object from a distance and I had to be practically on top of it to finally spot it. There was a lot of guessing, jumping, not finding anything on one mushroom, and then climbing the mountain to start all over again.
The spore pets are lovely in color, but they have a balloon-type syndrome. That is, instead of free floating like a spore should, they're currently tied to a rope (like a balloon). Hopefully that will be sorted out prior to WoD's release. XD
Ding! One thousand
The last bit of progression I've made on the beta is probably the biggest one. I finally unlocked the level 3 Menagerie! Whew. After collecting all of the available wild pets, I still had about 300 Draenor pet battles to complete. Using a tip from @patf0rd about single pet fights that still existed, I cheesed the rest of my way to 1000.
Once I finished the achievement, I purchased the level 3 blueprint and was all set to take a firsthand look at the new daily quest. It completely replaces the previous daily quest available from the level 1 and 2 Menagerie, but only for your toons that upgrade to Menagerie level 3. Side note, once you've unlocked the blueprints, all of your characters can purchase it (regardless of faction) if eligible. Hooray for only having to complete the achievement once!
Mastering the Menagerie has the same objectives as the daily it replaces, but the rewards are much better. In addition to the same number of Pet Charms, you also have a chance to loot one of seven new pets from the Big Bag of Pet Supplies. The pets don't have a 100% droprate and seem to be randomized (they don't correspond to the pet you have to defeat for that day).
Oddly enough, the daily isn't account-wide so if you have multiple high level toons with a level 3 Menagerie, you can increase your chances of getting the new pets. Another reason why WoD is feeling more and more like the expansion that "forces" us to spread our time across many different characters. But that's a different discussion. ;P
Doing the daily on two toons the first day (an alliance and a horde) only netted me one pet, the Sunfire Kaliri. Absolutely gorgeous!
On the second day, I scored two pets, one from each daily reward bag. Puddle Terror and Ghastly Kid.
These pets ARE cageable, so I expect to see these pets up on the AH quite a bit. I'm sure if you power through and reach level 3 Menagerie early in the expansion (and on multiple toons), you could make some decent gold by selling these MtM pets. I don't play the AH all that much, though, so I'll probably just hang onto the pets and any duplicates I get. Maybe I'll hand them out as gifts? :)
If undergoing the 1k Draenor pet battles grind doesn't sound like it's something you want to do, you could just wait until these pets pop up for sale. I don't think there's any prerequisite to add them to your Pet Journal. They probably won't be cheap initially; it's up to each collector to determine which one is worse: 1k battles or paying an arm and leg. For me, I'll probably just do the grind.
There are only seven MtM pets unfortunately, so I can't imagine this content will last us for very long. Especially for those that have many characters that complete the daily. Blizzard could always add more pets as drops from the daily to keep us interested, but that's probably only a temporary solution. We'll see what happens.