Mark Zuckerberg and his Facebook team spent an entire afternoon Tuesday explaining their new ad strategy to an audience of big-name corporate advertisers and Manhattan media. But as a series of high-profile executives from Blockbuster (BBI), Verizon (VZ), Coca-Cola (KO) and other new Facebook advertisers paraded across the stage, no one talked much about the Achilles heel of Facebook Ads: Facebook members.

Facebook is letting them control what advertising they see but also making members the unpaid purveyors of its clients’  brands. For the new form of advertising to work, members have to be willing to participate.

With Facebook Ads marketers can do three things: build their own profile pages to connect with Facebookers; use the Facebook news feed to broadcast updates of consumers’ interactions with brands to their friends; and analyze the Facebook members’ behavior to improve ad targeting.

Marketers can only advertise once consumers decide to “friend” a company or brand through its profile page. In theory, this sounds like an ideal way to build brand awareness, but will Facebook users actually do this voluntarily?

Maren Dougherty, a 23-year old San Diego resident with 400 Facebook friends pointed out that Facebook’s ad system couldn’t possibly work for every brand. “I can’t imagine saying I’m a huge fan or Best Buy or something,” she said.

On the other hand, casually sharing information about products like movies and music with friends makes some sense, Dougherty said. After all, that’s what Facebook users already do on with their profiles.

Even so, if Facebookers know that associating with a brand, even casually, will translate into marketing messages, will they still do it? The common theory among analysts and the social networks themselves is that people want to define themselves through their favorite brands.

That may be the case, but it doesn’t mean they want to sign up to be brand ambassadors.

Damon Brown, a 31-one year old Los Angeles writer and editor,  said he’s a huge hip hop fan and not opposed to touting the latest Kanye West album on the various blogs he maintains. But he draws the line at overt advertising. “It’s a whole separate thing for me to be affiliated with Rockefeller Records or Kanye West,” Brown said. “If the point is to have a viral, organic feel, you can’t manufacture it and that’s hard for advertisers to understand.”

Advertising analysts responded favorably to Facebook Ads, though not without noting how complex the strategy will be to implement.

Emarketer senior analyst Debbie Williamson said the promise of social network marketing has been to tap into the way messages spread virally from person to person. “What Facebook is doing is trying to extend that to make word-of-mouth part of marketing online,” she said. “It’s a big, complicated undertaking and there are a lot of moving parts that need to fall into place.”

Facebook, however, has a knack for introducing features that spark an initial backlash among members but that eventually become accepted. It first happened in September 2006 when Facebook opening up its gates to members outside of the college crowd. That same month, Facebook introduced the news feed, inciting uproar among some members who thought broadcasting their activities to friends and the friends of friends was intrusive.  Yet none of those changes did anything to slow Facebook’s growth from about 12 million users almost a year ago to nearly 50 million now.

Time will tell if Facebook’s bold advertising scheme will be tolerated, and more importantly, perform as planned. On the first point, the social network may not have much to worry about.

“This wouldn’t stop me from using Facebook,” said Sarah Baicker, a 23-year old graduate student at Northwestern University’s Washington, D.C., campus. “I don’t think anything can make us stop using Facebook at this point. It’s so engrained in the culture.”