If your Wordpress 2.1 is slow...
I just debugged a strange issue with this Wordpress 2.1 blog. It's running 2.1.2 to be exact, but I think the problem manifests itself with all 2.1.x versions. My site was running really slow - 40-50 seconds per page load. I had just moved it to this new host which is also running a few Rails apps. The Rails apps were running fast, so it wasn't the box.
I checked top and it showed the box was fine. I bounced Apache and MySQL. Still slow. I tried static pages - those were fine. I tried a phpinfo page - that was fine.
I googled and googled and finally found this Wordpress thread: [resolved] Update a post and blam.. every pageload is 20 seconds. The solution? I had to add www.luisdelarosa.com to the /etc/hosts file. I guess WP 2.1 has some sort of reverse DNS code in it.
So - if your Wordpress 2.1 site is slow, add your blog's hostname to the /etc/hosts file. You could also backtrack to Wordpress 2.0.1. I'll have to look into moving over to Mephisto sometime.