Found in 3 comments on Hacker News
alttab · 2011-10-12 · Original thread
Read this: http://www.amazon.com/Rails-AntiPatterns-Refactoring-Addison...

Easiest mistake in large rails apps is to let your controllers get too thick...

cicatriz · 2011-08-05 · Original thread
The book Rails AntiPatterns addresses many: http://www.amazon.com/Rails-AntiPatterns-Refactoring-Addison...