&#62; being able to implement things 10x more quickly than your competitors is a sustainable competitive advantage.<p>The only way you are going to get 10x, with roughly equivalent people is if someone is using a wholly inappropriate language (Ruby vs Forth for web apps, say), or if you can avoid writing libraries because someone has already written them.<p>This is one of the positive network externalities involved in programming language economics: the more people involved, the more likely it is someone has already written the code you need.  Of course, these effects are not so strong that everyone gravitates to only a few languages, but they are certainly a consideration.<p>By writing your own language, unless it makes it very easy to take advantage of some other language (the JVM languages are a good example), you are pretty much guaranteeing that you will have to do this work yourself.