I just got my invoice from them and got charged more than I expected. When I called for an explanation, what I learned is that if you delete a list, it remains on their servers for 30 more days. And you get charged for those subscribers.
The guy told me it's because they get people who accidentally delete lists or change their minds later and so they keep them around for 30 days. He said you can call or email them if you're sure and have them remove that list forever without having to wait the extra 30 days. It would have saved me about the price of a tank of gas had I known that. Now I do. So do you (if you didn't already).
I'm not big on small print. ADD, ya know.
Also, just because I asked and want to pass it on, you are not charged for people who sign up to your list but never confirm. They remain in the Aweber system for 30 days, but then drop off automatically if they never confirm (assuming you use confirmed opt-in). You're not charged for those people who don't confirm.
And finally, you must remove those who unsubscribe because they do still count toward your grand total (which is how they determine billing). I thought that was strange since you can't contact those people any longer, but I guess they keep charging for them because they're still on the servers. I think Aweber should be removing them once they unsub automatically, but it's not my call.
So there you go. Some of the finer points of not gigging yourself with extra fees at Aweber. Hope it helps!