I don’t know since how long, but I just found out that there’s already a stable version of MySQL to run on OS X “Leopard”. You may find a download link at this URL.
I haven’t installed this new version yet, but as I red it fixes all the issues from the previous versions, particularly the one about having the MySQL extension in the preferences pane of the system. This new version is also supposed to run better and faster on Intel based Macs. Well, let’s see, I’ll update this post as soon as I have done some serious testing with it.