Vim substitution feedback using vim-over
It is common while in vim to perform substitution tasks over the text you are editing. This is often accomplished using the following command:
:%s/<find>/<replacement>/g
The %s command will perform substitution over every line within the buffer. The /<find>/<replace> specifies the substitution to perform. Finally the /g indicates that this should apply to multiple occurrences if they are present on the same line.
This works great, although there is little affordance in determining whether the specified <find> will hit the matches you are interested in. The aforementioned command is a all-or-nothing with respect to execution, there is no visual feedback until you execute the command.
The vim-over plugin provides a dynamic approach for visual feedback while performing substitutions. It is extremely useful while crafting specific <find> patterns.

I have three vim maps that I use to simplify and enhance my substitutions.
This mapping (<leader>s) will find and replace the text under the cursor using vim-over for visual feedback. After the mapping has been executed you are left where you simply type the <replacement>/g.
nnoremap <leader>s :OverCommandLine<CR> %s/<C-r><C-w>/
This mapping (<leader>v) will perform a global substitution using vim-over for visual feedback. After the mapping has been executed you are left where you type the <find>/<replacement>/g.
function! VisualFindAndReplace()
:OverCommandLine %s/
:noh
endfunction
nnoremap <Leader>v :call VisualFindAndReplace()<CR>
This mapping (<leader>v while in visual mode) will perform a substitution only within the visually selected text using vim-over for visual feedback. After the mapping has been executed you are left where you type the <find>/<replacement>/g.
function! VisualFindAndReplaceWithSelection() range
:'<,'>OverCommandLine s/
:noh
endfunction
xnoremap <Leader>v :call VisualFindAndReplaceWithSelection()<CR>