Old way to toggle words, I no longer use it.

gistfile1.vim

" }}}2   ToggleTextOption    {{{2

" http://vim.wikia.com/wiki/Toggling_yes-no
function! ToggleTextOption()

  let w = expand("<cword>")
  call RegStash(1, '"') | normal yl
  let c = @" | call RegStash(0, '"')
  let pairs = [
        \   ["true", "false"],
        \   ["0", "1"],
        \   ["yes", "no"],
        \   ["on", "off"],
        \   ["and", "or"],
        \   ["??, "??],
        \   ["show", "hide"],
        \   ["left", "right"],
        \   ["before", "after"],
        \   ["absolute", "relative"],
        \   ["decode", "encode"],
        \   ["asc", "desc"],
        \   ["define", "undef"],
        \   ["exclude", "include"],
        \   ["if", "unless"],
        \   ["blank", "present"],
        \   ["while", "until"],
        \   ["first", "last"],
        \   ["in", "out"],
        \   ["get", "post"],
        \   ["to", "from"],
        \   ["only", "except"],
        \   ["foreign_key", "primary_key"],
        \   ["inspect", "to_yaml"],
        \   ["add_column", "remove_column"],
        \ ]

  let c_orig = c
  if     c=="+"      | let c="-"
  elseif c=="-"      | let c="+"
  elseif c=="<"      | let c=">"
  elseif c==">"      | let c="<"
  else               | let c=""
  endif
  if c != ""
    exec "normal r" . c
    return
  else
    let c = c_orig
  endif

  if match(w, c) >= 0   " cursor should not under a keyword
    for pair in pairs
      if w == pair[0]
        let w = s:ToggleTextOption_caseToggle(w, pair[1])
        break
      elseif w == pair[1]
        let w = s:ToggleTextOption_caseToggle(w, pair[0])
        break
      endif
    endfor
    if w != "" && w != expand('<cword>')
      call PosStash(1)
      exec "normal! \"_ciw\<C-R>=w\<CR>\<Esc>"
      call PosStash()
    endif
  endif

endfunc

fun! s:ToggleTextOption_caseToggle(in, out)
  if a:in =~ '^\u*$'
    return toupper(a:out)
  elseif a:in =~ '^\u'
    return toupper(strpart(a:out, 0, 1)) . strpart(a:out, 1)
  else
    return a:out
  endif
endf

" nnoremap <silent> <LocalLeader>a :call ToggleTextOption()<CR>