"We know he was working on his Web site while he was working on our clients' Web site," Hornick said. "There's no evidence that he had this idea before he met our clients."
ConnectU launched in May 2004, and has struggled to compete with the far more popular Facebook. The Winklevosses and Narendra sued Facebook in September 2004. The case was dismissed on technical grounds earlier this year, but ConnectU's lawyers promptly filed another lawsuit.
The costly legal battle began three years ago, before Facebook exploded in popularity and value, and it is not clear how much money the plaintiffs will get if they win, said Goldman.
He said strength of ConnectU's claims would depend on how a jury decides the particular facts of the case.
Though the possibility of selling Facebook may create pressure to settle the case, the time and expense that has already gone into the lawsuit suggests that it may be about more than money, Goldman said.
"Given how much has been spent, this could be more of an emotional concern, someone feeling like they've been jilted," he said.
Hornick, the ConnectU attorney, said, "The only way [to settle] is if they make an offer large enough to make my client happy, and I don't know what that amount will be."
When the lawsuit was originally filed, "The idea was that it would quietly go away," said Noah Kagan, who left Facebook last year and who says he knows Zuckerberg and the Winklevosses. "Facebook is now going to have to address it."