Here is a moving article on some of what goes on in animal shelters. Those of you who know me know that the one constant in my life (other than love of family) over the last eight years has been my shelter kitty, Scully. The thought of giving her up for anything is unfathomable to me (and actually bringing tears to my eyes...or maybe that's just that UNC is losing and I have them winning it all...kidding, it's Scully). I cannot imagine the reasoning in a person's head that leads to giving up a pet, though this article has a couple of examples.
If you're looking to get a pet of any kind, I recommend at least visiting a shelter and spending some time with pets there. You can often find young puppies or kittens in addition to the older pets (they estimated Scully at 9 months). Definitely worth a look, despite the risk you may want to take all the animals there home with you. Scully says, "Go Tarheels!" I mean, "Thank you!"