Michel Barbosa has a written a bachelor thesis on Rails adoption Results that jumped out at me:

• Q22: 95.9% would still adopt Rails, knowing what they know now.
• Q26: On average, companies have completed seven projects since adoption, with only (Q30) an average of two full-time Rails employees.

I didn't see the summary for Q7 ("When did the company start using Rails?"). That's too bad. If the average company has completed seven projects already, then they either adopted Rails 2+ years ago, or they are completing a new project per quarter.