First of all the basics -- as you know, there will be three kinds of talent trees, depending on the type of pet you use: damage, tanking, and utility. Damage seems pretty straightforward, tanking seems to imply that hunter pets may be able to fulfill the role of main tanks in 5-man instance, and utility conjures up images of crowd-controlling several enemies at once. There will probably be a number of talents which buff your pet's ability to do its designated job, as well as one or two usable abilities. At the very least, each pet will have one unique ability, depending on which pet family it belongs to, hopefully ensuring once and for all the No Pet Left Behind policy that players have been asking for since the beginning of time, in which none of our poor animal companions are any longer entirely without hope of being useful in any way whatsoever.
Mania's Arcania analyzed the problem of hunter pets and their uniqueness some time ago. At the time, she said she'd settle for a moderate improvement over the current sad state many pets are in now, but in the end it looks like Blizzard decided to go all the way and serve up some some righteous justice to the cause of pet variety -- taking these new pet abilities into account, hunters will probably be the one class with the most variable set of abilities and choices to make regarding how you want to specialize your character -- so, if you want to play a class capable of distinguishing itself from anyone else in the game in one way or another, then the Hunter will be the class for you. Assuming, as it appears now, that each pet family's basic ability will be useful in one way or another, you should be able to pick any one family and have a skill that can distinguish you from other hunters out there. There will certainly be some abilities min-maxers generally regard as "the best" and "the worst," but people with a bit of ingenuity should be able to offer something special with whatever pet strikes their fancy.
Some of the abilities currently hinted at on the alpha client include specializations for all sorts of various situations, which provide lots of inspiration for your hunter daydreams. They include a slowing ability, an area damage and armor reduction, an area hit-chance debuff, a self-heal, a spell interrupt, extra stuns, a knock-back, a disarm, and a rooting ability.
That's all the time I have this week to write about the new pet talents, but it's still a playground for the imagination. Feel free to run wild in the comments below! What sort of pet talents abilities do you dream of?