<xsl:for-each select="//node[guid=9012]">
<xsl:value-of select="."/>
</xsl:for-each>
When the current node is a <node> element, doing node/guid means child::node/child::guid, and your <node> element doesn't have a child called <node>.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference