So, most of the time I'm using Qt Creator, some of the time I use geany and the rest I use vim. I probably sholdn't have mentioned gedit as I really don't use it often. I'm planning on dumping geany in favour of vim next time I have to set up my development environment (basically when I get a new laptop, hopefully real soon) as I've been meaning to practice my vim skills for a while now. I was real good at it a few years ago, but then I got a little rusty, which is why I ended up using geany for python and plain text instead...
Actually, to be completely accurate, I use MPLAB too ;) I use it exclusively to program C for the PIC24 microcontrollers. I also used Notepad++ for AVR development a few months ago - if I had been developing on linux, I would have used vim, but I really dislike gvim, so do not use it on windows. I use MPLAB for PIC development because it integrates with the hardware programmer, the remote debugger and saves having to set up paths for a gcc thats not compatible with the one I use for desktop C++ development (though I plan on switching to clang, so I won't have any gcc clashes anymore then).
On the other hand, to my eyes at least, most other IDE's look something like this [6], [7] or very very extreme cases [8]. That is, they lose a lot of vertical space to tool bars.
When I'm developing on Linux and I'm not developing a Qt GUI application in C++, I use a mixture of text-mode vim, geany and gedit in a tiling window manager (that is, the "dock windows" in most IDEs are windows that I have tiled, or vim panels) with no window borders or decorations whatsoever [9].
[1] http://upload.wikimedia.org/wikipedia/commons/4/4d/QtCreator...
[2] http://www.developer.nokia.com/Resources/Library/Porting_to_...
[3] http://linux.leunen.com/wp-content/uploads/2009/03/qtcreator...
[4] http://lists.qt.nokia.com/pipermail/qt-creator/attachments/2...
[5] http://4.bp.blogspot.com/-teVIBJ45OEU/Twbi9_wQd_I/AAAAAAAAAY...
[6] http://www.eclipse.org/screenshots/images/SDK-RedFlag_Linux....
[7] http://www.hanselman.com/blog/content/binary/WindowsLiveWrit...
[8] http://swtswing.sourceforge.net/screenshots/images/EclipseMe...
[9] Not my screenshot, but similar: http://static.milkbox.net/ss/ss-2009-05-06.png