$.extend is a very useful function but it is hard to remember what is happening because depending on the arguments that you give it, it does completely different tasks.

Here is what I do to remember

ObjectUtils =  {
    deepCopy: function(obj){
        return $.extend(true, {}, obj);
    },
    copy: function(obj){
        return $.extend({}, obj);
    },
    update: function(base, override){
        //any keys in overrides that match keys in base will now
        //point to the override data.
        //any keys in overrides not in base will also be added to base
        //NOTE: no copies here! only updates to base
        $.extend(base, override);
    },
    augment: function(base, extensions){
        var args = Array.prototype.concat.apply([{}], arguments);
        return $.extend.apply($, args);
    },
    deepAugment: function(base, extensions){
        var args = Array.prototype.concat.apply([true,{}], arguments);
        return $.extend.apply($, args);
    }
 });

I know there are probably more things you can do with $.extend but these are very common tasks that could be highlighted with a simple wrapper function name.