Mastering the Emacs key bindings and its built in functions will allow you to manipulated text faster than IDE's such as Eclipse or Visual Studio.
Don't take my word for it, check out these videos of pros using Emacs.
Once you get to a decent level in Emacs you can effectively edit any language: Java Script, Java, Ruby, Python, HTML, C, C++, etc.
Getting started with Emacs is a pain in the butt, the out of the box experience is worse than bad. Emacs default configuration does not expose the Emacs newbie to the more powerful features (hippie-expand, etags, yasnippets, etc) of Emacs. I suggest started with the Emacs Starter Kit dot files.
Another reason that Steve Yegge claims that the world best programmers use Emacs, is elisp. Elisp allows the experienced programmer the power to easily expand Emacs. Writing an extension in Eclipse or Visual Studio is significantly harder than writing a quick function or even a new minor mode in elisp.
