Most startups need to focus where their market is. If you're in B2B or focused on selling something to startups, you need to be on Twitter.
If you're more of a general consumer product, you should be on facebook, but not on a fan page, you should be trying to get users to "Share" your content.
Fan Pages can be a good way to communicate with existing customers or blog visitors, but it's not really an acquisition mechanism.
Sure it is. We have 1000 fans on Facebook, and basically none of them have converted to our paid service yet. It's people who came to our site and hit "Like". Many of them don't even use our free service. Status updates we post there can absolutely convert users.
And when those users like an item in our feed, or comment on it, that potentially goes into their feed, which is outreach to their friends (i.e. new customers).
If you're more of a general consumer product, you should be on facebook, but not on a fan page, you should be trying to get users to "Share" your content.
Fan Pages can be a good way to communicate with existing customers or blog visitors, but it's not really an acquisition mechanism.