How to completely uninstall MySQL (community edition) on Mac OS X Snow Leopard
I needed to get my development version of MySQL into sync with the version installed in production, so I had to uninstall 5.1 and install 5.0 instead. This used to be easy, but now that I’ve upgraded to Snow Leopard, every time I tried the MySQL install was telling me that I couldn’t install because there was a newer version already installed. It continued showing me this error no matter what files I removed and how many times I restarted (just in case). In the end it turns out that instructions for uninstalling that were written for OS X Leopard (10.5) don’t work on Snow Leopard (10.6), because Apple moved the location for installer receipts.
I found the correct instructions at SilverTab’s Corner.