List building is only one aspect of building an online business. Important? Yes, but not for the purpose you might be thinking of.
I'm in no way discouraging you, but if you do go along that path, keep in mind that you are at the end line of this trend. I prefer being ahead of the trends.
Basically, you need more than just building a list nowadays. I just don't want you to waste any time trying something that's already been tried and exploited to death...
Take care,
Bernard St-Pierre
Marketing Consultant
Copywriter/Teacher