The match_selection is a nice addition to Sublimetext2. When you select a word in a file all other instances of that word are also highlighted so you can see at a glance everywhere else in the file that the selected word is used.
A nice extension to this would be if you code use some key combination that would initiate an editing session so that changes made to the selected word would be reflected in all other instances as well.
I know we have search/replace but this would be quicker. If this feature already exists can someone point me to it please.