It's been up for a couple of days now and there are just over 100 fans at the time of writing. The good part is that about 20 of them are people who are not my Friends on Facebook, but have become fans following someone else's suggestion. Obviously, when you set up a Page, the first people to invite are your friends but for it to be successful you need to get them referring other people and thus increase traffic through the links. Already I've seen a sharp increase in traffic from Facebook.
Before you go ahead and set up a page, though, I think you need to know if it's genuinely going to interest people. This is why I did it with Greek recipes - people are into food! I wouldn't do it with this blog, for example, as I don't feel it would be offering something different from any number of other Pages.
There are a large number of niche blogs out there that I think would benefit from having their own Page on Facebook and a resultant increase in traffic. But as I said above, the thing is for it to be attractive enough for people who are not your Friends to become fans.