I prefer to use double opt-in on most of my sites. It is true your list will grow as much as 33% faster with single opt-in, but down side is your going to have more spam complaints and more bounce backs.

Personally I hate getting spam complaints, they are always a pain to deal with. Bounce backs can also begin to be a problem depending on how much server power you have.

Charles, that’s another reason why I don’t really like Aweber, when running your business having another company tell you how to do it rubs me the wrong way.