HTML5shiv now ships with Core

Drupal now ships with built-in support for HTML5 elements in IE 8 and below by including the HTML5 Shiv library. In addition to including the HTML5 Shiv, the addition of jQuery 1.7 also takes care of supporting HTML5 Element in IE8 and below via AJAX calls. (This essentially removes the need for using the innershiv plugin.)

The HTML5shiv JavaScript will be added to any page that contains any JavaScript. You can also add the shiv manually with the example code below:

drupal_add_library('system', 'html5shiv', TRUE);