That's a pretty cool plugin, although I always prefer to run the MySQL server with --general_log when debugging, that way I also catch the naughty plugins by-passing $wpdb calling mysql_query directly :)

Quick note -- queries are logged into a publicly accessible directory. This is a mistake many plugins do/did, even fairly popular ones like W3 Total Cache, which at some point stored database and object cache publicly accessible on disk. You definitely don't want to leak your database queries, which can contain e-mails, password hashes, authentication tokens to external services like Twitter, Google, etc.