"Paul, I have a rather serious issue to discuss with you, according to our contract I owe you over 30% more of the business in late penalties which would give you over 80% of the company," the alleged email says. "Mostly, though, I just won't even bother putting the site live if you are going to insist on such a large percentage. I'd like to suggest that you drop the penalty completely and that we officially return to 50/50 ownership."

If the emails that Ceglia cites are legitimate, they could cause a lot of legal and financial woes for Zuckerberg, who just this week fended off a separate case challenging his ownership stake in what has become the world's largest social networking site.

"This [the amended Ceglia lawsuit] could be serious trouble for Facebook," said Dan Olds, an analyst with The Gabriel Consulting Group. "The attorneys representing Ceglia aren't small-town lawyers. They're a big-time firm that has a lot of experience with tech companies. I would assume ... they've done their due diligence and are confident that sufficient evidence exists to give them a reasonable chance to win."

Olds added that if Ceglia was to win this court case, it could not only give him a huge chunk of Zuckerberg's immense fortune -- estimated at $13.5 billion by -- but could also give Ceglia significant control over how the company is run.

It's likely though, said both Olds and Zeus Kerravala, an analyst with Yankee Grop, that Zuckerberg would pay big bucks to make sure it never happens.