I've been using Vim, full-time, for nearly three years. I have written a lot of plain text in that time.

Pretty early on, I noticed I was wasting a lot of time with several common typing patterns. For example, to type "I've" requires 5 key strokes including two stretches of the little fingers. I replaced that with the abbreviation iab iv I've. That's only two keys instead of five and it doesn't put any unnecessary stress on the little fingers (which I sometimes have problems with).

I created several other abbreviations for common typing patterns (mostly avoiding having to type apostrophes and capital letters). Here is a small sample:

iab i I
iab iv I've
iab il I'll
iab dont don't
iab monday Monday
iab february February
iab cof CoffeeScript

I keep these English-only abbreviations in a separate file (~/.vim/abbreviations.vim) which gets sourced when editing Markdown or text files.

Some people also like to add common typos to their list of abbreviations. I have a few of those but I like to keep them to a minimum. When possible, I prefer to force myself to re-type the word correctly so that I learn the proper spelling.

Annoyances

This worked well for me for a long time but it had two problems that kept bugging me. One was that I had to manually add the capitalized versions of all my abbreviations. For example, iab cant can't as well as iab Cant Can't. This duplication of information was annoying and felt messy.

The other problem was that it was a pain to add new abbreviations. I had to manually open up my abbreviations file every time.

I was about to start creating my own script to deal with this stuff. Thankfully, one already exists.

Abolish plugin

The Vim Abolish plugin is pretty neat. Read the tutorial for a full walkthrough of the features. It lets you do stuff like this:

" Typing the following:
Abolish seperate separate

" Is equivalent to:
iabbrev seperate separate
iabbrev Seperate Separate
iabbrev SEPERATE SEPARATE

It has more advanced features which allow you to group together related words:

Abolish cal{a,e}nder{,s} cal{e}ndar{}

Also, if you place a ! at the end, you can add words to you abbreviations file easily:

" In ~/.vim/abbreviations.vim (or where-ever you like)

" `expand('<sfile>:p')` gets the absolute path of the 
" current file that this is being executed from
let g:abolish_save_file = expand('<sfile>:p')

if !exists(":Abolish")
  finish
endif

" Typing `:Abolish! im I'm` will append the following
" to the end of this file:
Abolish im I'm

There is also a Subvert command for doing similar things in search and replace:

" Will replace "Facilities" with "Buildings", etc.
:%Subvert/facilit{y,ies}/building{,s}/g

Again, check the GitHub repo for more details. I haven't been using the plugin for long but I really like it so far.