Facebook is always looking for interns (SW Engineering isn't listed on the intern page but I'd be very surprised if we were already full).
http://www.facebook.com/careers/ http://www.facebook.com/careers/department.php?dept=interns
http://www.facebook.com/careers/ http://www.facebook.com/careers/department.php?dept=interns
(This is a throwaway account, but I'd love to get in touch.)