The company has taken its beef with aggregator Power.com into federal court, where Facebook has sued for a host of claims. Power.com allows users to access information from across social networking sites in one central location -- an ability that Facebook clearly thinks threatens its own hold on the information that users have uploaded to their profiles.

In the lawsuit, Facebook alleges that Power.com's scraping system violates copyright and trademark laws, CAN-SPAM and California state law. Among other claims, Facebook says that Power.com induces Facebook members to provide their user names and passwords in violation of Facebook's terms of service. Power.com then allegedly contacts users' friends by sending emails that appear to have come from "The Facebook Team."

Facebook has made these types of allegations before. When ConnectU founders sued Facebook's Mark Zuckerberg for allegedly stealing the idea for the site, Facebook fired back with a lawsuit accusing ConnectU of scraping the site for email addresses. The whole mess eventually settled, but not before a court dismissed some CAN-SPAM claims, but left open some state law claims, Internet law expert Eric Goldman reported last year. In fact, Goldman reported, these types of email harvesting claims date back at least 10 years to a dispute between eBay and the rival company OnSale.

Overall, the state of the law is still unsettled. In the five years since CAN-SPAM became law, courts have reached different conclusions about what type of activity violates the statute. In addition to the CAN-SPAM allegations, Power.com is also accused of violating Facebook's copyright and trademark -- but the law in that area also isn't clear.

Power.com has already responded that it will try to use Facebook's approved platform, Facebook Connect, by the end of this month, which is probably all that Facebook really wanted to see happen here.

Still, it's hard to know whether Facebook users will react well to Facebook's flexing of muscle here. The site is still drawing new users; on Christmas Eve it garnered its highest share of traffic ever, according to Hitwise. With every new user, Facebook potentially gains access to a trove of information that can be used for marketing and advertising purposes.

Facebook obviously wants to control the flow of that information, ranging from users' email addresses to their tastes in movies and music. But if the site takes enough heavy-handed actions that undermine features members find useful, people might not stick around on the site for long.

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