This is really just a jsf question, but you can acheive this just like exporting to html - with one key difference, you must include the f:view tag with a content type of text/xml. Although I have used facelet templates with this technique, I assume the examples below can easily be adapted.

Note 1: You can specify content types other than text/xml - if you do, make sure the f:view encloses your output document - facelets will only parse valid xml.

Note 2: This will not work with icefaces - its direct to dom rendered expects a dom tree with root element of html (haven't checked this with 1.6 releases though).

Note 3: Seam now provides a way of outputting pdf documents using jsf tags - see seam docs!

Example 1: outputting xml

<?xml version="1.0" encoding="utf-8" ?>
<myXmlRoot xmlns:t="http://myfaces.apache.org/tomahawk"
 xmlns:f="http://java.sun.com/jsf/core">
 <f:view contentType="text/xml" />
 <t:dataList var="rowData" value="#{results}">
 <myItem>#{rowData.description}</myItem>
 </t:dataList>
</myXmlRoot>

<f:view contentType="text/csv"
 xmlns:f="http://java.sun.com/jsf/core"
 xmlns:t="http://myfaces.apache.org/tomahawk">

"First Item", "Second Item"
 <t:dataList var="rowData" value="#{results}">
"#{rowData.item1}", "#{rowData.item2}"
 </t:dataList>

</f:view>