Migrating favorites

For anyone interested in this thread, I have figured it all out. Here is a modified (generalized) version of the function I wrote. Obviously, your SQL statements will be different depending on how your legacy favorites information is stored.

function migrateFavorites() {
	global $wpdb;

	$userstable = $wpdb->prefix . "users";
	$usermetatable = $wpdb->prefix . "usermeta";
	$postmetatable = $wpdb->prefix . "postmeta";

	// ---------------------------------------------------------------------
	// --- Find and loop through each user with favorites
	// ---------------------------------------------------------------------
	$sql = $wpdb->prepare("SELECT * FROM <table> WHERE ...");
	$results = $wpdb->get_results($sql);
	if (!$results) {
		echo msg("No users found to migrate","warning");
	} else {
		$count = 0;
		foreach($results as $result) {
			$count++;
			$username = $result->username;
			$user_id = $result->ID;
			$usermeta = get_user_meta($user_id, "simplefavorites", true);
			// -----------------------------------------------------------------
			// --- Get all favorites for this user
			// -----------------------------------------------------------------
			$sql = $wpdb->prepare("SELECT * FROM <table> WHERE ...");
			$getfavorites = $wpdb->get_results($sql);
			$newposts = array();
			foreach($getfavorites as $favorite) {
				$post_id = $favorite->post_id;
				$newposts[] = intval($post_id);
				// -------------------------------------------------------------
				// --- Increment the favorites count for this content_id
				// -------------------------------------------------------------
				if ( ! add_post_meta( $post_id, 'simplefavorites_count', 1, true ) ) {
					$postmeta = get_post_meta($post_id, 'simplefavorites_count');
					$newcount = $postmeta[0] + 1;
					update_post_meta ( $post_id, 'simplefavorites_count', $newcount );
				}
			}
			// -----------------------------------------------------------------
			// --- Now add or update usermeta table
			// -----------------------------------------------------------------
			if (!$usermeta) {
				$favorites[] = array(
					'site_id' => intval("1"),
					'posts' => $newposts
				);
			} else {
				$favorites = $usermeta;
				$existing_posts = $usermeta[0]['posts'];
				$allposts = array_merge($existing_posts, $newposts);
				$allposts = array_unique ($allposts);	// --- avoid duplicate posts
				$favorites[0]['posts'] = $allposts;
			}
			$error = update_user_meta( $user_id, 'simplefavorites', $favorites );
			if ( get_user_meta($user_id, 'simplefavorites', true ) != $favorites ) {
				echo msg ("An error occurred' favorites","error");
			} else {
				echo msg ("Finished migrating $count users' favorites","#666");
			}
		}
	}
}