This might or might not be related, but my WP 2.7 install broke under the weight of more than 2,000 queries spawned by the more fields plugin. Most look like this (from a dump of the more fields settings screen):
Query: SELECT * FROM wp_posts WHERE ID = 1647 LIMIT 1
Time: 0.00081110000610352
Caller: require_once, require_once, require_once, require_once, do_action, call_user_func_array, more_fields_object->flush_rewrite_rules, WP_Rewrite->flush_rules, WP_Rewrite->wp_rewrite_rules, WP_Rewrite->rewrite_rules, WP_Rewrite->page_rewrite_rules, WP_Rewrite->page_uri_index, get_page_uri, get_page, get_post
Query: SELECT post_parent
FROM wp_posts WHERE ID = 1544 LIMIT 1
Time: 0.00067400932312012
Caller: require_once, require_once, require_once, require_once, do_action, call_user_func_array, more_fields_object->flush_rewrite_rules, WP_Rewrite->flush_rules, WP_Rewrite->wp_rewrite_rules, WP_Rewrite->rewrite_rules, WP_Rewrite->page_rewrite_rules, WP_Rewrite->page_uri_index, get_page_uri, get_page, get_post, _get_post_ancestors