As of approx. October 6, 12:30 AM EST GMT -5 Facebook HTTP services seemed to have gone down.
Ping tests were successful during this time, however, attempts to load the website resulted in timeouts.
More updates tomorrow morning after some official announcements have been made. My initial speculation is botnet and/or DoS attack but this is very preliminary.
Update 12:49 AM EST GMT -5
Looks like downrightnow.com is down as well…
Update 10:15 AM EST GMT -5
Some other sites also seem to have gone down, reddit, apple store and digg among others.