Couple of days ago I've installed the facebook like buttons on my blogs.
Also in Google Analytics it started to show some duplicated pages with ?fb_xd_fragment parameter.
In fact this is a bug regarding to the Internet Explorer users (at least untill version 8). Even more it breaks the page is some ocasions after clicking on the "like" button.
1) Use the iframe like button code when the user is using Internet Explorer.
2) Hide the button for the Internet Explorer users.
In both cases you can use my post on How to Detect Internet Explorer with PHP
You can prevent duplicate URL from your Google Analytics stats.
Edit your account and exclude the fb_xd_fragment parameter.