According to Mashable (http://mashable.com/2008/03/06/google-advanced-search/), Google reorganizes and simplifies the advanced search form. While the changes are not available to all users (for whom it is not clear).
Some of the rarely used input fields are hidden in the additional drop-down section: But inside this section: These changes are not available to me either, but as far as I noticed, some changes are already presented on the advanced search page - www.google.com/advanced_search?hl=en
Or have I not used advanced search for a long time? :)