This whole druid thing is pretty fun, and just keeps getting better. To get the aquatic form, you first need to turn level 17, and then a quest giver in Auberdine starts you off on a little quest chain that ends up with you running all over the place, swimming to collect a few items, and then you get your new shape shifting capability.
This is really the way to do it. I like the quest chain so much more than just visiting a trainer and paying a few bucks to get a new skill.
For Hunters, we had the level 10 pet training quests. And I think that's it. If I remember correctly, there was another Hunter quest in the 50's that took you all over Azshara and then into the Sunken Temple. But that wasn't for any new capabilities, it was just for some nice piece of gear.
I hope the new expansion has more stuff like this for different classes, because it really makes you feel like you earned the new skill, and not just "ding level, pay trainer".
Some of the very unique Hunter capabilities like Freezing Trap and Misdirection really could benefit from a nice little chain of quests that introduce you to the skill, and maybe also try to teach you the usefullness of the skill at the same time.
Of course, in terms of return on investment for Blizzard, class-specific quests are money they spend on developing content only limited audience will ever experience, so I won't hold my breath.