I do mostly Java and C/C++ development, but I'm starting to do more web development (PHP, Rails) and Eiffel (learning a new language is always good).
Currently, I use Eclipse for Java, C/C++, and Ruby (not Rails). Since I know the environment, I'm thinking that it would be easier for me to find a plugin and use Eclipse for all of my development languages. But are there cases where a language-specific IDE (EiffelStudio for Eiffel, as an example) would be better than Eclipse?
I have used many many IDE's and in most cases to me it breaks down to personal preferences. Sometimes the language specific ones have some addins/addons/features that are nice but unless they are things you can not live without you should go with what is most comfortable for you.
I would think that if you are comfortable with the multi-language IDE it would be better to stick with that one. This way you dont have to memorize multiple IDE layouts, keyboard shortcuts etc.
Mastering an IDE takes time and energy. Using a multi-language IDE is definitively beneficial for a programmer who needs to develop in several languages. It is for the same reason that tools like VI and Emacs are so popular.
On the other side, IDE specialized in one language could sometimes go much further on some aspect and could be the preferred choice in some situations.
I love Eclipse as Java IDE (so much that we decided to build some Eclipse based application) and I'm an Emacs fan. But I also like the Groovy support of IntelliJ and the efficiency of EiffelStudio.
It's a matter of taste, you forgive the ones you love...