Would you still use Facebook if it started charging its users?

If Facebook started charging a monthly or annual fee, would you still use it? I know some people who get a lot of value out of it, and I know some who use it only because it's free. I wonder how much their user base would decrease? Increase? After speaking with a friend, he said "It depends." If it was like $1 a month, then it would be worth it. Anything more, then it would not. What would be your dollar/currency threshold?