Pros and Cons of Doggy Doors?

Now that we're getting a second dog, one of the questions we've been asked is whether or not we're going to install a doggy door in our back door.

Over the years, we've heard mixed reviews on doggy doors (always a draft in the house, security issue versus convenience), so for those of you who have one or had one back in the day, please weigh in!

[ Photo from Liberal Handyman]