jgwebber pointed out that the new maps.google.com is using the XSLTProcessor at the client side. This is interesting... while I always thought it is possible, I didn't saw too many cases where this approach is actually useful beyond academic exercises.

As an example, here is the stylesheet used by google: http://maps.google.com/mapfiles/homepanel.xsl

And here is a sample XML being processed:

<?xml version="1.0" ?>
<page>
 <title>pizza in atlanta</title>
 <query>pizza in atlanta</query>
 <center lat="33.748888" lng="-84.388056" />
 <span lat="0.016622" lng="0.017714" />
 <overlay panelStyle="/mapfiles/localpanel.xsl">
  <location infoStyle="/mapfiles/localinfo.xsl" id="A">
   <point lat="33.752099" lng="-84.391900" />
   <icon image="/mapfiles/markerA.png" class="local" />
   <info>
    <title xml:space="preserve">Kentucky Fried Chicken/Taco Bell/<b>Pizza</b> Hut</title>
    <address>
     <line>87 Peachtree St SW</line>
     <line>Atlanta, GA 30303</line>
    </address>
    <phone>(404) 658-1532</phone>
    <distance>0.3 mi NW</distance>
    <description>
     <references count="9">
      <reference>
       <url>http://www.metroatlantayellowpages.com/pizzaatlanta.htm</url>
       <domain>metroatlantayellowpages.com</domain>
       <title xml:space="preserve">Atlanta<b>Pizza</b> Guide-Alphabetical Listings of Atlanta<b>...</b></title>
      </reference>
     </references>
    </description>
    <url>http://local.google.com/local?q=pizza&near=atlanta&latlng=33748889,-84388056,11825991348281990841</url>
   </info>
  </location>

  { lots more locations... }

 </overlay>
</page>

Then, the generated HTML will directly render in your web page. In the end, the web traffic is kept at a minimum since all you transfer is a small XML as opposed to a bigger HTML.