It's really beside the point, and it's a shame that Twitter's scaling woes are at all associated with Rails. Rails is a framework for making web applications. How many of Twitter's problems stem from generating HTML pages? At its core, Twitter is a massive messaging system; the web app part is a tiny layer on top. Blaming Rails for Twitter's downtime is like blaming your chat client if AIM goes down.
QOTD:"It is important to keep in mind how useless this information is."
His math looks like it's really inflating the scribd numbers. Could compete.com really be off by a factor of 5?