I identified the "getOtherNamespaces" function in wikiPage.php as a major bad guy. It is used to link to the appropriate Talk namespace in the sidebar and the footer. On my test installation, returning no other namespaces (an empty array) cuts the time to generate a page in half! (Tested with the "Biology" article using ab -n 20 -c 4)
I don't have time right now to fix this, someone please!!!!!!! help :)
Magnus