said by Boogeyman :

Its well established that most BBR users know that user accounts and passwords are good ideas. But I'm talking about Joe Average. Its been my experience that even when average users set up user accounts, they are rarely used correctly. While visiting family a while back, I went to use my grandfathers pc and he just old me his account password. My aunt and 2 cousins also had thier own accounts, but everyone knew my grandfathers (admin) password and whenever thier account wouldnt let them do something, they logged into his and did it. The same situation goes on at my brothers house (who isnt related to the other family). I know its not everyone, but its been more common in my experience than the people who use them correctly.

I know they probably wont ever give an ad revenue discount, but my point was that if they did, it would give them a huge PR boost and make many people WANT to opt in to the service. It wouldnt even need to be monetary discount. For the people who actually use thier ISP email/webspace, a bump in storage would be enough for a lot of people to want to opt in. See, if they bundled it with something users wanted, most everyday users would opt in if they judged the pro to be better than the con.