WordPress slow? Check your plugins MySQL database. I’ve checked the slow-log and discovered some slow queries.

I did some very basic adjustments, maybe not all very well overthought, but with dramatically speedup results.

wp_ratings checks a lot on both rating_postid en rating_ip, but by default no index so:
Slow Queries:
SELECT rating_username, rating_rating, rating_ip FROM wp_ratings WHERE rating_postid = 487;
SELECT rating_ip FROM wp_ratings WHERE rating_postid = 487 AND rating_ip = '';
ALTER TABLE `wp_ratings` ADD INDEX ( `rating_postid` )
ALTER TABLE `wp_ratings` ADD INDEX ( `rating_ip` )

wp_term_taxonomy from the very powerfull plugin YARPP (related posts plugin) as explained in http://wordpress.org/support/topic/192707 misses an index
Slow Query:
SELECT t.*, tt.* FROM wp_terms AS t INNER JOIN wp_term_taxonomy AS tt ON t.term_id = tt.term_id WHERE tt.taxonomy IN ('category') AND tt.count > 0 ORDER BY t.name ASC;
ALTER TABLE `wp_term_taxonomy` ADD INDEX ( `taxonomy` )

wp_options doesn’t have an index on autoload (a core query), but the next query runs lots of times. Of course it is cached, but why not speed it up as much as possible.
Slow Query:
SELECT option_name, option_value FROM wp_options WHERE autoload = 'yes';
ALTER TABLE `wp_options` ADD INDEX ( `autoload` )

Any comments are very welcome, this are just quick and dirty solutions, that perhaps need more time and study, but for now i’m happy!