Re cloned bug - this issue is to track what is still not previewable (and whether it should be / can be etc).
.*xml and *.xsd files are still not previewed, other content types seem to be previewed fine.
Validated on Alfresco 3.1 build 211,
Windows 2008 SP1, Tomcat 6.0.18, Mysql 5.1.34, JDK 6u7, IE7, FF3