Whenever I read articles about Rails performance I often think about the saying from the early days of Twitter, "Rails doesn't scale". However as most of the co

Whenever I read articles about Rails performance I often think about the saying from the early days of Twitter, "Rails doesn't scale". However as most of the comments have said here, the biggest factor that typically affects an app is I/O. There are plenty of large companies that run Rails and for most up and coming startups Ruby on Rails is probably enough to validate your idea.