I agree that it's the main service where you should pay for quality and quality varies. What I dislike about aweber is that the model of paying for the total number of subscribers you have just doesn't make sense. If I don't mail in a month, I've been charged just for them holding some names in a database.
The billing should be based on some flat rate plus a price per mail. That way, people that like to not mail their list too often are not penalized.
Maybe with other flat rate plans for those that mail frequently.
Oh and you have to be sure to clear out unsubscribes cause they charge for those too.
Regarding people being on multiple campaigns, yes it sucks that that costs more too. Another argument for the billing being proportional to total mails sent. Amazon services get it right in the main. I wonder if they plan an autoresponder - that WOULD be something to look out for I reckon. Some more competition. Most of awebers features aren't needed by most people.