I am one of the people that do the System Design Interview at the company I work for, and I would say that “How to Design Twitter”, as presented here, is a poor interview question. It has a number of problems:
IME, a good System Design Interview Question requires a question that is well specified but has a lot of possible answers. Even specifying you want to make a newsfeed service like Twitter for 1 million users with an average request rate of blah blah is more than enough to fill an hour long interview. This blog post gives a poorly specified question with a lot of possible answers. I think if one went into a System Design Interview as an interviewer after reading this blog post they would not be prepared to evaluate a candidate.
Author might want to consider how to design a blog with better backend database uptime. ;)
It took me a full minute to realize that this was the (intentional) joke. :)