There are still some questions as to whether or not Facebook can live up to its astronomic valuation, but advertisers should find some comfort in a new report from comScore. In the second installation of its ongoing "Power of Like" series, the research firm found that advertising on Facebook can indeed generate increased sales, though there are some important caveats to consider.

comScore's white paper, titled "The Power of Like 2: How Social Marketing Works," shows that users who are fans of certain brands on Facebook, as well as the friends of those fans, are more likely to purchase items than those who are not. Fans of Target, for example, were 19 percent more likely to complete an in-store purchase after being exposed to a Facebook ad. Friends of Target fans, meanwhile, were 27 percent more likely to purchase products from the retailer. A case study on Starbucks showed similar results: fans and their friends were 38 percent more likely to complete an in-store purchase after being exposed to a Facebook ad. Compared to the average web user, Amazon's Facebook fans spent twice as much money at the online retailer during the holiday season.

The report also examined the effect of paid advertising, finding a 56 percent increase in online purchase incidence for an anonymous Facebook advertiser, along with a 16 percent rise in in-store purchases. It's worth noting, however, that this part of the study was commissioned by Facebook itself.

Also significant is the fact that comScore's study included only those companies that agreed to participate, so its results could be skewed, and may be difficult to extrapolate. Nevertheless, comScore says its statistics show that marketers can translate Facebook exposure into financial gain, through more focused ad campaigns that encourage "consumers to purchase or engage with the brand."