We once had 2 links on HN front page for http://backspac.es for the better part of a day -- although neither made it to number one spot -- running only 1 dyno. Something like 18K uniques.

Also had two techcrunch posts about something I made (http://venturecrapital.us) running on a single micro ec2. tornado + nginx + mongodb and proper indexes go a long way. Similar traffic.