Zed Shaw has compiled a long list of suggestions on how you can get your manager to let you use Ruby on Rails for your next project. It’s full of goodies including this strategy of dealing with the ill-informed ‘does it scale’:
For example, they say, “It needs to handle 500 connections/second.” Don’t let them say “users”, “users” means nothing. Then you go test their current WizBangOMatic and find it only handles 10 conn/second. You can then come to them and say that Rails can’t do 500 conn/second, but it can do better than the WizBangOMatic which only has 10 conn/second performance. It’s evil, but it puts the performance harpies at rest.