I like to follow up on Why You should learn PHP by rumblinglankan.com which talks about PHP for bloggers and extend it for programmers in general.
I was a full blown Java developer back in the day. I knew many developers who stuck to their guns and did one thing like Oracle, Java or .NET and said it would never go away and there would always be a market for it.
Well things change. Windows administrators are learning Linux, VB6 guys probably moved to VB.NET etc. If you sit still your skills will become obsolete.
A few years ago I saw the potential of PHP. It was simple to learn widely deployed on the Internet. I started building some Intranets with it, thinking I can move some of that logic out to a website later.
That was back in 2005. Now more than 50% of my work day is PHP, MySql, drupal, Code Igniter, WordPress or something other than Java. If I locked myself into Java I wouldn’t have got most of the projects or opportunities I got.
Now I use PHP from writing system scripts to extending drupal. I’m also thinking about trying PHP GTK to write a Windows GUI application.
Look around and try something. Software is always changing, try to keep up.