Ghostery blocks a list of trackers such as google analytics, KISSmetrics, and facebook social plugins[1]. Ghostery generally won't affect the page at all except in invisible ways, but it will remove Like, Tweet, +1, etc buttons to prevent requests from being made to Facebook/etc.

You can also fine-grain set Ghostery to allow certain trackers, like Google+ buttons, while still blocking all the others.

[1] The tracker that this article is about.

P.S.: Watch out as Ghostery doesn't actually work on Chrome. See https://news.ycombinator.com/item?id=3034093