Show Me the Money!
Before ARIA
<div id="ads">
...
</div>
<div id="nav">
<form id="searchform" ...>
<input name="query" value="" />
</form>
</div>
<div id="content">
AJAX content inserted here...
</div>
After ARIA
<div id="ads" role="banner">
...
</div>
<div id="nav" role="navigation">
<form id="searchform" role="search" ...>
<p class="error">You did not enter a search term</p>
<input name="query" value="" aria-required="true" aria-invalid="true" />
</form>
</div>
<div id="content" role="main" aria-live="assertive">
AJAX content inserted here...
</div>