This whole thread smells of lack of understanding of software. Hackers should know how inefficient an SQL server would be to handle Twitter-type tasks, versus specialized code. This is supposed to be hacker's news, not small business news.

news.YC is a good example of an efficient architecture. If it was written in Ruby/MySQL, pg would need at least 20 servers to keep up with the current traffic, versus a single box now. And the latency would never be as good as it is now.