Lastnight I found myself in a situation where I needed to know which mounts and pets my alts knew, but found myself in the embarassing position of not being able to give any intelligent response. If someone had asked me what recipes / patterns etc my characters knew I would have been fine. The same could be said of which items each character owned.
Cutting to the chase:
This got me thinking that there is a need for a mod that tracks what mounts pets each character has learned and presents the information in simple way. And then I thought, hey wouldn't it be great it it worked along the lines of ProfessionsBook / RecipeBook but for mounts and pets, with "Already known for <characters>" and "Can be learned by <characters>" when ever a pet or mount tooltip appears.
I would love this. I've seen a couple minipet addons so far but nothing that really does what I need. Like you said a system more like the many existing tradeskill moniters would be ideal. Just a list of whats available where, which chars know what and some tooltip info would be great. :)