In case you haven't heard, today is Adopt the Internet Day! My cats have come through a Human Society foster home (hi Sue!), a Craigslist post, and a classified ad in a town newspaper, so I don't have personal experience with Petfinder.com. However, I do encourage those considering adding a pet to their lives to think about adopting shelter animals, or animals who might otherwise end up in a shelter.
For example, the handsome fellow pictured below is available at the Tacoma Humane Society. As a black cat, he is statistically less likely to be adopted. Poor little dude doesn't even have a name yet.