1. KDE - it's the best looking, very well integrated (i.e. in terms of applications fitting together nicely), and as of version 3.2, is extremely responsive.
2. ee - Laugh all ya want, but it's what I used as a newbie and it does everything I need from a CLI editor. Nano if I can't get ee.
3. Firefox - is there any other? :wink:
4. Xine - as long as you have the necessary libraries / codexes, you can watch (almost) any video file format. I use Noatun for listening to music, but that's just because it's a simple audio player for KDE; I don't have a strong bias for it.
5. Any proprietary video formats, particularly quicktime and *especially* .wmv / .asf. Microsoft have done a fine job screwing everyone over that doesn't run Windows for watching .wmv files.
6. Binary packages. Specifically, .debs. Why struggle with compiling when I can do dpkg -i <package> and be done with it?
7. It really varies; I use CLI a lot but it's nice to have a GUI when the CLI tools get really complicated. One nice option is to have the utility for system administration be CLI but then to have the *option* of using a GUI. In Libranet, adminmenu runs from the command line but xadminmenu functions as a front-end for it.
8. Nope. I have a dual-boot system for when I absolutely have to use Windows.
Hope that helps!