One of my first jobs ages ago was to convert a large Perl codebase to ASP 2.0 because my new boss, a 22 year old CTO, was replacing a guy more than twice his age and Perl was "for old folks" as he put it. This one person turned the whole company into a Microsoft dev shop with one decision simply because he didn't feel comfortable around Perl code.
COO at a previous company did this, went from Java to .Net shop. This was two years ago. Laid off most of the Java developers, brought in consultants. I had left, but there were some really intricate business processes in that code base, running on a 40 node jboss cluster. They embarked on a rewrite, which of course is taking longer than promised. All the Java developers who could, got jobs and left, now there are only two guys left who know how to deploy to the the cluster. And they use scripts, they don't understand anything they're doing. The competent people left long ago.
