Just recently, and may have been with the wordpress 3.2.1 update, this plugin started giving a red "error" when clicking the like button. It still works fine on sites that are not on the multisite wordpress network installation. Clicking the "error" gives a popup with this message:
"There was an error liking the page. If you are the page owner, please try running your page through the linter on the Facebook devsite (https://developers.facebook.com/tools/lint/) and fixing any errors."