Also, I found a relatively easy method of adding parent_page classes to the parent pages when appropriate. It is simple actually:
In the same way you can identify a current page by using is_page to determine what page is currently showing, you can identify parent_page in the same way.
The example below shows a scenario where an About page exists with a child page set in WP Pages called About Sub Page.
The About page code is set to display current_page_item in its class if we're viewing the About page or will display current_page_parent if we're viewing the About Sub Page. If there are more sub-pages, then simply add more identifying is_page code to the parent class as needed.
This then allows me to set my button image sprites to remain in the rollover state to indicate the current page AND to keep drop menus displayed when in parent sections.
More info and code for fancy drop menus for Thematic are referenced here:
http://themeshaper.com/wordpress-menu-tricks/
http://forums.themeshaper.com/topic/create-horizontal-dropdown-child-menu-that-holds-on-subpage
Here's the code example:
function childtheme_menu() { ?>
<div id="menu">
<ul>
<li class="<?php if ( is_page('about') ) { ?>current_page_item<?php } else { ?>page_item<?php } ?> <?php if ( is_page('about-sub-page') ) { ?>current_page_parent<?php } ?>"><a href="/about/" title="About This Blog">About</a>
<ul>
<li class="<?php if ( is_page('about-sub-page') ) { ?>current_page_item<?php } else { ?>page_item<?php } ?>"><a href="/about/about-sub-page/" title="About Sub Page">About Sub Page</a></li>
</ul></li>
<li class="<?php if ( is_page('advertising') ) { ?>current_page_item<?php } else { ?>page_item<?php } ?>"><a href="/advertising/" title="Advertise on My Blog">Advertise</a></li>
<li class="<?php if ( is_page('contact') ) { ?>current_page_item<?php } else { ?>page_item<?php } ?>"><a href="/contact/" title="Contact Me">Contact</a></li>
</ul>
</div>
<?php }
add_filter( 'wp_page_menu', 'childtheme_menu' );
