http://www.workingwithrails.com/high-profile-organisations yell.com is also pretty high profile, but not listed.

Rails is not Ruby.

You got that wrong: ruby is not Rails, but Rails is ruby.

Meaning: any app using Rails is using ruby, so this list matches. OTOH, any app using ruby doesn't necessarily use Rails, so the other way around wouldn't work.

Working with Rails is a subset of what the OP was asking.