WYSI_NOT_WYG when developing things with graphical interfaces. It's fine to use vim or whatever for programming an algorighm or designing a class, but when it comes to visual web development an IDE is the way to go. Rapid prototyping, easy debugging, and even drag-and-drop components are all available. I'd like to see vim or emacs do that...
I actually use nano, bluefish, or scite for all of my rails development, and then make the css using the FF web developer toolbar, pasting it into the necessary file when I'm done tweaking.