Using the Devel module I discovered that the default mysql configuration parameters were slowing drupal down.
To see where your mysql is installed type at the command line:
The selection of configuration files are in share/mysql; or if you followed the above instructions for installing MySQL, it should be in /usr/local/mysql/support-files.
The configuration file is in etc/mysql4; or if you followed the above instructions for installing MySQL, it should go in /usr/local/mysql but is not there by default. You can put it there by copying it in:
sudo cp /usr/local/mysql/support-files/my-large.cnf /usr/local/mysql/my.cnf
Restart MySQL for the new settings to take effect.
To view the current variable settings for MySQL, from the terminal command line client type:
mysqladmin -uroot -p variables
I opted for the "my-large.cnf" settings and halved the sql query times.
You can monitor MySQL through a pleasant user interface using MySQL Administrator, though it seems to expect my.cnf at /etc/my.cnf (it will still work, you just can't view the conf file).
I also discovered that I could roughly halve page load times by using Apache 2 instead of the stock Apache on Tiger. To see what version you are running:
I downloaded the php and Apache 2 from ServerLogistics: http://serverlogistics.com/downloads.php.
I am not sure I can recommend this for production sites as I do see some error diagnostics I haven't resolved yet. I didn't expect such a big difference with Apache2. Measurements with a system call profiler show that it does about half the read(2) system calls as Apache 1.3.
The overall impression I have from my benchmarking is that drupal pages require a lot of disk I/O to synthesize. Anything you can do to speed up or miminize (e.g. caching) is going to help. MySQL already has plenty of caching if a my.cnf files is being used. For the Apache/PHP part busy sites will need a php accelerator.