Jason - doesn't seem to be working. I can see that the cached images have been created and are located in the designated cache folder, but the src attribute is still pointing to the original (unresized) images.
My code now looks like this -
<?php foreach ($galleryRecords as $galleryRecord) { ?>
<li><a href="_img/gallery/<?php echo $galleryRecord['filename']; ?>" class="p7lsm_type_img">
<?php
if(TRUE){ // Begin Cached Resized Image: ImageCacheInstance_1343838442669
ob_start();
?>
<img src="_img/gallery/<?php echo $galleryRecord['filename']; ?>" alt="<?php echo $galleryRecord['alt']; ?>" height="240">
<?php
echo(getCachedResizedImageHTML(ob_get_clean(), "_img/gallery/cache", "proportion", "", false));
} // End Cached Resized Image: ImageCacheInstance_1343838442669
?>
</a></li>
<?php } ?>