These findings come in the wake of last month's IPO and reinforce investors' concerns that Facebook has not yet found an effective way to monetize its 900 million-strong user base. And some advertisers apparently share those concerns. Though Facebook made $3.7 billion in revenue last year, its sales growth is slowing. Indeed, General Motors, the United States' third largest advertiser announced last month that it would no longer pay for advertising on Facebook. "[The survey] shows that Facebook has work to do in terms of making its advertising more effective and more relevant to people," eMarketer analyst Debra Williamson said.

In the meantime, Facebook continues to evolve in an effort to keep users coming back. New features such as the "Timeline" interface and the planned $1 billion acquisition of mobile photo-sharing app Instagram are both examples of such efforts, Gartner analyst Ray Valdes told Reuters. "Facebook continuously has the challenge of Facebook fatigue, of the novelty factor wearing off, and therefore they have to introduce new kinds of interaction."