A day in the life of a slow page at Stack Overflow
Tuning SQL is key, the simple act of tuning it reduced the load time for the particular page by almost 50% in production. However, having a page take 300ms just because your ORM is inefficient is not excusable. The page is now running at the totally awesome speed of 20-40ms render time. In production. ORM inefficiency cost us a 10x slowdown.