The main turnoff for me when it comes to Rails is watching other major companies like Twitter completely rewrite their application away from Rails.

Growing pains -- the kind of pains we all want to endure some day. If you are planning to grow, why wouldn't you start with something you know has an end game (like PHP or Java)?

The often cited slowness of Rails, mixed with companies rewriting their codebases, and the flurry of vulnerabilities in the past year has caused me to take Rails less seriously.