When reporting the Content-Type of an XML document (such as in the HTTP response headers) use "application/xml", rather than "text/xml".
The reason for this is because the first line of your XML document should tell the client what the encoding of the document is anyway.
<?xml version="1.0" encoding="charset"?>
If you were to use text/xml, you'd need to report the character set there, and this could conflict. You may end up with an HTTP response that looks like:
HTTP/1.1 200 OK
Date: Wed, 11 Jun 2008 20:48:36 GMT
Server: Apache/1.3.41 (Unix) mod_jk/1.2.4 PHP/4.4.7
Content-Type: text/xml; charset=iso-8859-1
<?xml version="1.0" encoding="utf-8"?>