Now, we can add a couple of new languages or environments to the mix. Some have been pushing Groovy, another servlet-oriented language. Despite the obvious Java-oriented scripting language proliferation, Sun has seen fit to launch yet another scripting language, JavaFX. Microsoft has also announced its scripting effort called Silverlight, despite have ASP.Net already.
I also think the open source and hobbyist communites feel compelled to develop new scripting languages because they simply don't like something about existing ones. It usually starts out with the need to have a language that solves a very narrow problem and expands into a general scripting language. Python and Perl comes to mind here.
Scripting languages are a very good idea. They allow for rapid, iterative, development, are exceptionally useful for user interface programming in browser-enabled applications, and make it much easier to deploy small applications quickly and with few resources. They also helped recreate programming as a hobby, something that was on the verge of disappearing as professional programming became more complex. We just have too much of a good thing and need to pare it down a bit. That way we can get on with writing code and not learning new computer languages.