Well, lots of people have already said lots of great stuff.. Already touched on a lot of my ideas, hehe... One other thing, i'm not sure was mentioned though, is what could have possibly occurred to the eggs before the players got there? Was the creature a natural supernatural baddy, or just a predator by nature? And either way, why was he in direct conflict with the players? I heard mention of a cult. Did the cult, and perhaps the leader place some form of spell upon the creature? If they did, have they already placed some form of preparation spell upon the children themselves, making them more malleable to the will of the master of the cult, or to make them natural monsters? Was this gem something natural, or something "attached" to the creature, and could this "trait" be bread through the eggs naturally?
Sorry if i touched on a lot of things that have already been hammered down... I did a glance over, a pretty good one too, but I'm tired as hell at the moment >.<
And for your second question, my gaming group has had a decent number of critter kinda pets going on... One of the ones that stick out most in my mind, is another I'd consider to be the most infamous...
It was a rather random occurance really... The GM had just a random encounter kinda idea... Honestly, he just threw something totally out of the blue at us, a Hippogryph of all things. It was night, in the middle of a raided village, on an open plain, before a tall, dark and very evil mountain, complete with castle/fortress to boot. The creature was completely out of place, and obviously meant to just be a quick fight. Instead, the Ranger tried to go out and make friends with it. That I'm fine with. But then, one of our less... Competent players drops her prepared attacks, as she realizes she can do something OTHER than fight it, and goes forward, ahead of the Ranger, attempting to calm it.. That would be fine, if the character would have had any business or any skills that would help in the manner. Instead, she was a very dumb, very narrow minded Paladin. And the GM, also being involved with said player, spent the next 5 to 10 minutes going through her character sheet, trying to come up with a roll that he could rationalize to himself, so she could "attempt" a roll of some sort. It ended up being something very silly, and he pretty much let her woo the animal far better then the poor Ranger, who was quickly pushed aside and ignored at this point. Several games later, no Feats or Skills taken to help her in her ways, she starts riding the intended encounter into battle, and through the air and all that fun stuff.
Basically, I'm perfectly fine with critters, and player doing things to surprise their GMs. The only time I start to get bothered with it, is when a player goes through the proper steps, the proper Feats, and the proper Skills, takes time and effort from his character to add something special, like a Cohort, or a special mount of some sort, gets completely and utterly overshadowed by a player who just randomly goes out and grabs a random, powerful/useful creature, and never bothers to work anything into their character sheet, other then under the Equipment section...