Well I use a plain text editor. It formats and colour-codes the text, has all usual text editor stuff, and it's mainly gedit on GNU/Linux and Notepad++ on Windows.
Project management, code completion, error checking while you write, and automated building with multiple build profiles. These are the advantages I see IDEs as having.
Project management isn't really necessary, I use a solid directory structure and store my project in a git repository.
Code completion would be nice (in fact there are plugins for it) but I've never cared enough to get it.
Error checking while you write is irritating and I'd turn it off. I've become very good at figuring out compiler and linker errors so I have little use for this.
Build management is great, but I am fine with a Makefile right now and will be fine with CMake or something if pushed to it.
I've noticed that people want to mention GNU/Linux as an IDE. It almost is, as what I describe (give or take the editor) is how most people on GNU/Linux manage projects. Still though, I think the 'plain text editor' option applies to these people.