If Facebook had it their way, users would come to the site and stay. Ads would send users to other areas of the social network. No one would ever leave. So it comes as no surprise that Facebook's latest ad strategy focuses on subtle ways to keep users in the network.

In the second quarter of 2011, Facebook's advertising department offered an interesting incentive to advertisers: If your ad kept people on Facebook, it would cost you 29% less than an ad that sent users out to another website. For the fourth quarter of 2011, Facebook offered the same deal and pushed the number up to 45% off. Given that Facebook does as much as possible to keep you on the site, will it eventually become your one true social network?

According to a the TBG report, some brands are responding to the lowered ad costs by building a presence within Facebook. Boston-based CraveLabs, whose tagline is "rethinking local advertising," focuses on getting customers to a business' Facebook page. "Why make your customers that find you on Facebook have to search for your website to find out what your best dishes are?" says CraveLabs, next to an example of why users should visit a restaurant's Facebook page instead of the actual website. A targeted ad that drives users to the restaurant's Facebook page would cost nearly 50% less than an ad that sent users out to the restaurant's website.

At the same time, Facebook ads that send users out to a website are getting more expensive. The report notes the average cost per click (CPC) has increased 10% versus other countries that only saw a 1% increase. The cost per thousand impressions (CPM) rates have increased by 8%, on average.

The most clicked-through categories for Facebook ads are food & drink and beauty & fitness are the top categories for most-clicked through, trailed only by retail, home & garden and not for profit.

At the end of last year, Facebook ramped up its advertising strategy. Every user has access to their own personalized Facebook adboard, which shows recently viewed ads, and the current selection of sponsored stories.

In the fight for the social Web, some say Google's latest addition of "Search, plus Your World" threatens Facebook. But if Facebook can steal eyeballs and clicks that would have normally gone to websites, will it win the battle of the social Web?