IMPORTANT UPDATE FOR 9.2
The "new hotness" feature for mounts has been completely rewritten to work better with how the game has operated the last several expansions. The problems were that 1) multiple new mounts are often acquired in a small window of time followed by periods of drought and 2) flying mounts are often acquired when the vast majority of time was being spent in ground mount only zones.
The result is that many new mounts never really get a chance to be highlighted by the system before getting bumped down into the full pool. The solution is to track multiple hot mounts. Now, when you acquire a new mount its given a heat value. When you summon a mount, we will first check that slider percentage to see if we should summon from the pool of hot mounts. If so, we'll select from amongst just those mounts with hotter mounts having a greater chance of being summoned. A mount summoned this way loses one from its heat value. When a mount hits zero its no longer hot and falls into the general pool of mounts.
This system should ensure that all new mounts you acquire will have their time in the sun with the most recently acquired mounts being summoned the most often.
USING POKEDEX - THE SHORT VERSION
The games Key Binding UI will contain a section for Pokedex. The only two commands you'll probably want or need to keybind are Toggle Mount and Summon Companion. SummonOtherMount is a useful bind for those times when you don't want the type of mount we selected (for example, we choose a swimming mount but you want a regular one). Pokedex configuration can be reached through the games addons menu or by typing /pd. The full list of commands can be found at http://www.wowace.com/addons/pokedex/pages/main/actions/.
Pokedex allows random summoning of mounts and companions using preference values set by user to influence selection. Pokedex will summon the appropriate mount, or invoke a class specific movement ability like Ghost Wolf or Burning Rush, based on what the current location and conditions support. Pokedex can also randomly set character's title using the same basic ranking system.
The chance of a particular item (mount, companion or title) being selected is equal to the rank you have assigned to it divided by the total of the ranks for all other eligible items. Put another way, each point of ranking is one ticket to the raffle drawing to see which mount is selected. If all items are still set to the default value, then they all have an equal chance of being selected. An item which you have assigned a value of 0 will never be selected.
Pokedex has support for all the normal ace3 profile stuff (change current, copy, etc), with a couple of twists so that you can have the benefits of sharing a profile and still be able to make character specific tweaks by overriding the rank value on that character. See http:www.wowace.com/addons/pokedex/pages/profiles/ for more info.
The New Hotness - The idea behind this feature is that your most recently acquired pet/mount/title is something you're probably excited about and what to see more often than the rest of your collection. Or maybe you want to flaunt it in front of the all the people who are still trying to get, for example, their Sinister Squashling. When dealing with large numbers of pets or mounts, even setting it to the max rank will not cause it to show up very often. So rather than make you downrank every other item, the hotness feature acts as a way to get that one pet or mount out more often. If there is a hot pet, we'll first do a percentile roll against the heat of hot item. If the heat is set to 50, then 50 percent of the time we would summon that hot pet. The other 50 percent of the time, we'll do the usual random selection out of the weighted pet pool.
Safe Dismount - This feature is disabled by default but can be turned on in Pokedex's options ui. This feature allows you to keep as a default behavior that of having the Auto Dismount in Flight option turned off, so that accidently trying to cast a spell in flight won't send you plummeting to your death, but allows you to choose override scenarios where you do want actions to dismount you automatically so that they can be executed. The scenarios you can opt into are 1) when you are in combat, 2) targeting something attackable or 3) attempting to gather a resource via mining, herbalism or skinning.
Random Titles - You can also rank titles the way you do pets and mounts and have Pokedex periodically change your title.
Auto summon pet - You can have Pokedex summon a non-combat pet, if you don't already have one out, every time you dismount or change zone.
Druid forms, Ghost Wolf and Burning Rush support - Pokedex supports using Druid forms, Shaman Ghost Wolf and Warlock Burning Rush in the appropriate situations as part of the Toggle Mount command.
autocast Water Walking when mounting - An option exists (off by default) for Shamans to cast Water Walking and Affliction Warlocks to cast a Soulburned Unending Breath as they summon a mount with the Toggle Mount command. This way the buff is already in place when they encounter water so they don't have to dismount, buff and then remount (all while wondering why Death Knights get to cast Path of Frost while mounted).
autocast Horn of Winter when mounting - For Death Knights, Pokedex can cast Horn of Winter whenever you mount. This is useful for keeping the buff up while questing or resource gathering (e.g. mining).