I have a problem with importer.
If categories have entites HTML, as "&" or "&" in name
During importing, Importer create "a zillion duplicate categories"
Because, in importer you clean title with
$categories[$cat_index] = $wpdb->escape($this->unhtmlentities(str_replace(array ('<![CDATA[', ']]>'), '', $category)));
And after the query return false...
Example : In DB you have
Category NAME : 'Toto & Blurps'
In Query (l.319) : 'Toto & Blurps'
"SELECT cat_ID FROM $wpdb->categories WHERE cat_name = '$category'"
See patch for one possible solution.
See XML for an example of the problem...