My favourite IDE is KDevelop. I use it for my larger projects because of a few features: it's really easy to switch between files with CTRL-/, look up functions with CTRL-ALT-M, and look up classes with CTRL-ALT-C (can't remember if I set up those shortcuts or not, though :P). It has auto-complete and that sort of thing as well.
I tend not to use many features of IDEs -- for example, I compile my code in a separate terminal and use the command-line gdb debugger -- but I still really like KDevelop.
Of Eclipse I can't say much. I don't really use it. I did get it working on my Debian system, can't remember how. I imagine I just hit "+" in aptitude. I do have both the Sun Java and gcj installed for Java runtimes (I think gcj is my default). I just don't really like Eclipse that much. It always seems like when I start using it I'll get a bunch of wizards popping up whenever I just want to create a new source file . . . and it's quite slow on my system as well. On the other hand, I think I'd probably enjoy it if I was using Java, because it has some really nice Java features (like refactoring and renaming of source files and so on).
