I think they are bad because they are annoying which makes a person close them faster then they would close a site they were viewing that had banner ads instead.
I don't mind google ads. They are nice because they are relevant to the page you are viewing. Popups are annoying and I feel aren't affective because I think most people are annoyed and X it out without even reading it.
Is google AdSense worth it? How much have you made from using the program? I was thinking of getting but was unsure whether or not it would be worth putting ads on my site in order to get little or no money.
Try to keep your prices reasonable. I don't know if you would make loads of money doing this but if your really good at templates then you can make money. It depends on the quality of your templates.