One consideration is that a powerful text editor can become a desktop user interface. That is to say, the texteditor is the one and only interface into the operating system. GnuEmacs and XEDIT(on VM/CMS) are the two closest text editors I know that fulfill this promise. You can start up GnuEmacs and stay in it all day. Do everything from reading mail to compiling programs. And because you're in the text editor, everything can be copied and pasted everywhere else.
XEDIT is used a little differently. It is used to build program front-ends. The equivalent to 'ls' on unix for VM/CMS is written by pumping directory information into XEDIT and remapping keys around. Thus, you get FULIST on VM/CMS, FILELIST is also implemented this way.
MultiEdit and SlickEdit are two other PC editors that you can live in all day.
Interestingly enough, this is a great way to learn portable habits. That is to say, when you are spending the day in your editor, you are using keychords and commands that are the same regardless of the platform you are running on. Emacs is a great leveler in that respect. You just need to have Emacs on all platforms. ;-)
This is philosophically opposite from UnixToolsPhilosophy embodded in ed and ViFamily editors.
However, you might say that the OberonEditorFamily has a mix of both philosophies. It has the sparseness of the UnixToolsPhilosophy but the power of the EmacsFamily as an integrator of tools.