Here's a little lesson that I learned regarding client side XML and processing it. If your app requires any XML processing over about 50 nodes, use a native DOM implementation.

My app stores some Google Map locations in xml. Each location has the lat/long and an info node that I process in my app with XSLT to create the html for the marker window. Well, one file has 700+ of these location nodes, and when I wrapped AJAX-XSLT using the GWT, it took 2 full minutes to download the file, parse it, and process each location.