Make sure the doggie door can be locked. I have seen it where other animals got into the house through the doggie doors and the family had to call the cops to get the other animal out.
I also wouldn't want my dogs to go out whenever they felt like it -- unless I had a big yard with a good fence and they couldn't get out of it in any way.
If your dogs aren't used to running outside on their own, unless you want to spend a lot of time training them to behave without you around, doggie doors might not be a good idea.