Guys, any property that you build on facebook is owned wholly by facebook not you. The moment you forget that you're doomed!
I have only just started this fan page malarkey and it is obvious that you need to monetize early. Don't wait till a page hits 50K fans before you start making money off it.
Monetize early! How you do it is entirely up to you. It's a 'fools errand' to build up a page before you try to monetize IMO. Facebook is fickle and her chief goal is always to protect her users. If you think FB doesn't monitor the activity of us marketers you are sadly mistaken. I believe 70% of facebook updates are driven by the need to protect it's users against spammers(marketers). And yes I do believe most social networks see marketers as spammers. That is precisely why fan pages in their current incarnation won't stay that way for long.
So, do yourselves a favour and monetize early!
Peace out,
T10