Facebook has become very good at integrating revenue streams into key user flows.... effectively creating powerful upsell opportunities. For example, when you create a Facebook Page, you are promptly greeted with dynamically generated ads to drive fans.
Below is the newest upsell / integration: when page owners post to their feeds, a prompt is given to "create an ad to reach potential fans with your post. You only pay when people Like or click to your Page from the ad." The ad is customizable but is a combination of your post's content and your page's formatting. Also compelling: Facebook presents estimated reach of those ads based on the proposed basic targeting - namely users who are not already fans AND are friends of fans.
I have been preparing a blog post on what I call placing products "in the river"... more to come on this, but this is a great example of delivering simple product to the right audience / user at the right time: