My nomination for the greatest interface breakthru of the 1990s: word processors that automatically underline mispelled words as you type them. Actual autocorrection is handy too, if it does only what you mean, and that's a big "if". Both autocorrection and typo-highlighting also assume you know when and how to turn on your wordprocessor's feature for "this is no longer English text that I'm typing, so stop spellchecking it -- yes, I know 'tyakawehtö' isn't in the spellcheck file!".
Everything else in word processing has been downhill tho. You wouldn't believe the hassle I went thru the other day trying to get WordPerfect to print in "journal preprint" style -- i.e., two virtual pages sideways on 8.5"x11" paper. The insane difficulty of it was reminiscent of word processors whose representational model of things (gleefully reiterated in its interface) makes no easy provision for "double-space this document!" -- and sometimes they even have no entry for the term "double space" in the help index.
I recently banished all the default "tool bars" (boo hiss) from my word processor's display, replacing them all with one small simple custom toolbar consisting only of these:
The first thing I always do with a newly installed word processor these days is go thru its Configuration menus and figure out how to turn off most of the features of the interface that weren't there in 1990, like the Dancing Paperclip that invites me to sit on his lap as he reads the help file to me. I don't like that Dancing Paperclip -- he did a bad touch on me!
Best feature of MSWord: getting it to stop saving files in MSWord format by default -- "Tools : Options : Save : Save Word Files As..." and RTF. RTF is not exactly an "open format", but it's better than the bloated core-dumps that pass for ".doc" files.
Best feature of WordPerfect: the "Reveal Codes" option. MSWord is crippled for lack of it.
I'm not exactly thrilled about either, but they basically came (free) with my (free) latptop.