Classifications of commercial websites

Web 1.0:
Sites = News/Articles/Entertainment
Advertising = Banners.

Web 2.0
BUSINESS
Sites which advertisers like because they have a perceived or actual value.
Search Engine, Internet yellow page site, Directory, Lead gen-site, Classifieds

CONSUMER
I've created a site which people like to use:
Email, Social Network, Online Game

Note that there is not a 3rd option: Mixed.
Only the top, well executed sites can pull off being both a consumer and business oriented site (ala Google, Craigslist). You cannot be "a social site that combines users and advertisers in a unique way..." as so many business plans these days content.

Sites which try to be Business and Consumer oriented generally fail at doing either effectively. History has shown, if you can build the users, advertising revenue will come. Pick your audience, love them and stick with them. Once you turn around and start pushing your users off to other sites (via ad feeds and sponsored links), it will lessen your value to users. Afterall, if the purpose of your consumer site to keep users satisfied on your site? If a sponsored ad is more engaging than your content, you've got a loosing strategy long-term.