Tools like this are useful because Facebook's own platform for this, Facebook Insights, runs three days behind, doesn't measure custom tabs or apps, and doesn't integrate with analytics for other digital marketing channels.
The tools work inside Facebook to provide detailed analytics data about applications, custom tabs, brand pages, contests and advertisements, among other things. This wasn't easy to achieve because most of Facebook (Fan Pages included) doesn't allow JavaScript, but Webtrends developed a custom API to get around that. Third-party applications built on the Facebook platform are easier because JavaScript is permitted.
The special features here are the ones related to comparing data between Facebook and other digital channels. For example, you can see how much traffic is being driven to your Facebook Fan Pages by Twitter updates, or you can overlay Facebook Fan Page activity with that on corporate blog posts.
Here are some images of Webtrends' Facebook tools in action.
