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.