I had no desire to start modifying the key event translations file. I recommend using a programmable gaming mouse and/or keyboard for programming complex key sequences. A programmable mouse/keyboard device make my work flow much more efficient, so they offset the relatively minor cost. They allow you to program single keys or key sequences using macros and automatically activate your custom profile when linked to an executable. Personally, I use the Razer Naga series mouse.

Many times you can reduce the [[ ]] abuse by using rules. For example when you use Cases instead of Select.

Besides that I have also made modifications to MenuSetup.tr in order to make () {} [] [[]] easier to type with single key shortcuts, but this is probably discouraged and not supported. For example:

        MenuItem["Matching [[ ]]",FrontEndExecute[{FrontEnd`NotebookApply[FrontEnd`InputNotebook[], "\[LeftDoubleBracket]\[SelectionPlaceholder]\[RightDoubleBracket]"]}],MenuKey["F8"]],

One more related idea: In many modern editors when you select something and type "(" then the selected expression becomes parentized. I wish Mathematica did that too.

Szabolcs, the above for some reason did not work for me, 10.0.2, windows 7. In the notebook, the left [[ show OK, but not the ]] one. I type Alt-[ and now I see [[ added automatically, but when I type Alt-] the notebook inserts [] instead of ]] I modified the file

C:\Program Files\Wolfram Research\Mathematica\10.0\SystemFiles\FrontEnd\TextResources\Windows Now it looks like this: (had to do it as Admin on windows)

Restarted Mathematica. Type Alt-] and get [] instead of ]]

As Rolf said, "Command" is a special key available only on Macs. On Windows I use Control instead of Command.

There are some reasons to use subscripts. For example, if I do symbolic solutions to problems with variables like x[1], x[2], and get rules such as x[1] -> expr1, etc. and then apply N to the rules, x[1] changes to x[1.], etc. That doesn't happen with subscripts.