I'm sure Rails is great for getting an application up quickly, but once you get some traffic and the application gets more complex surely you'd end up hacking it so much you might as well have written from scratch in PHP or similar?
That article just confirmed that I made the right decision when staying well clear of Rails.
There are plenty of large sites e.g., yellowpages.com and urbandictionary.com (which switched from PHP) which are built using Rails.
Even if you have scaling problems that are around that of, say, Twitter, your application code still isn't your bottleneck; talking to your database is. No amount of framework (or lack thereof, as you propose/promote) will save you from the ramifications of poorly-constructed SQL.
Surely the best defense against this is writing every query yourself rather than letting Rails do it? (As implied in the article).
My argument isn't Ruby execution speed vs PHP execution speed, it's Ruby writing it's own SQL vs me writing it.
I agree 100% that the database is usually the bottleneck, it certainly is for my site.