It's not as if...
...the service that FR provides is in any way worth the money. Back when it was free, I signed up and used it to see what my old school and work mates had got up to. But as soon as the FR management came up with the idea of trying to charge for it, I not only stopped using it, but had my details removed altogether.
As a freebie, funded by advertising revenue or whatever other form of third-party financing that they could come up with, it would have been fine. But it wasn't ever something that was sophisticated enough or important enough to me (or to many other folks I suspect) that I would be prepared to pay directly out of my own pocket to have access.
That's the problem with most of the current Web 2.0 shite that's out there. They can be an interesting idea and they offer services that can sometimes be useful for staving off a bit of day-to-day boredom, but most of them don't have enough immediate and direct value to their users that those users would be prepared to pay for it up front.
It's so simple that even I can understand it - if you want to charge for a web-based service of some kind, you've got to start by thinking of a service that people will, in general (or eventually), be prepared to pay for. While a freebie site all dressed up in pastel colours and with rounded borders might generate a lot of interest out there in the blogosphere, you'll only really know if it's got financial legs when you try to charge for it directly and find out whether people are actually prepared to dip into their own pockets for what you're providing.
Ten bazillion free subscribers doesn't mean jack unless you really can convert them to direct paying customers or you have some other rock-solid way to generate revenue off the back of it. Seems like FR falls at both hurdles.