Actually, I use vim as an IDE. It does everything *insert IDE of choice here* can do. If not, you can write a plugin in a large range of languages to add the features you require. I can also run my full blown vim IDE in a terminal, which you GUI IDE weenies cannot do :-D
Vim also has syntax highlighting support for a huge range of languages too - more than most editors and IDEs. Personally, I use vim to edit text files, bash scripts, C, C++, Java, Python and Factor source files and it integrates well into my toolkit.
As an editor, vim provides powerful tools and shortcuts to manage text editing quickly and efficiently providing more conveniences (though they are hinderances until you learn them, of course) than most other editors I have tried. As an IDE, it provides me with everything I could want from an IDE: syntax highlighting, code completion, tabbing, code folding, multiple text buffers (actually, how many editors/IDE's do you know which support multiple paste buffers?), split windows, build tool integration, file browser, source control integration and much much more - and all of this can be run in a text terminal! (You can also run it in a GUI, but I'm not really a fan of it tbh. Also, theres versions of vim such as Cream which hide the modal-ness of vim by default, which makes it easier to learn and use) How is this not an IDE?