According to a number of reports on our forums, coupled with confirmation by the team, there appears to be an issue with Facebook notifications and the "Me" tile. The issue is it seems as though the notifications sent through get caught up and continuously alert the user to the same content.
Some of our readers have stated that the service corrected itself over time and now functions as it should (while others have to resort to clearing notifications via the Facebook app), but it still remains to be a particular annoyance to many. We're not sure as of yet whether this is due to Facebook's service or with Microsoft servers.
We previously had issues with Twitter notifications back in January, so this is nothing new unfortunately. Be sure to let us know in the comments, and join in the discussion over at our forums, should you be experiencing issues as well.