As fast-growing Facebook closes in on MySpace in the U.S. in terms of unique visitors later this year, it's burning through millions of dollars a month (some claim it's as high as $20 million), with no magic levers to reverse the trend in the short term.In November 2007, when Facebook took a $240 million stake from Microsoft, the investment was at a $15 billion valuation. Now it's down to $4 billion and probably less. As Caroline McCarthy reported a few days ago, rumor has it that "one potential investor submitted a term sheet for a valuation in the neighborhood of $2 billion."As Facebook works its way toward a probable IPO, the big question is: how can it show it can make money? Well, one way--and I'm not the first to suggest it--would be to charge a nominal monthly fee. With that in mind, I ask a simple question: how much would you be willing to pay to use Facebook per month?A lot of people I ask say they'd pay $1 a month--or, preferably, a yearly fee of $10 if paid in one shot. But some say they have Facebook fatigue and would rather quit than pay a dime.
