I ran into problems when trying to get Joomla to run on PHP5 and reverted to PHP4. I don't recall the specifics at this point, but don't currently see a need to update. I was able to get Joomla to run on MySQL v5.0.16 with just a simple change. I wrote about it on my site, which is running on Dreamhost with the configuration I just mentioned. It also runs fine on my home machine using Apache on Windows.
The link is included simply so you can evaluate the performance of the site with MySQL5. I have also pasted a description of the fix below. Link:
http://benconley.net/cms/content/view/26/37/
From my site:
I started using MySQL 5, and was unable to save any new data in Joomla. For a long time I thought this was a problem with my installation. but eventually I found that it was an incompatibility with MySQL 5. The upcoming version of Joomla addresses the compatibility issues, but I didn't want to wait that long. It turns out that disabling strict SQL mode in the MySQL configuration solved my problem. Simply open your "my.ini" file within the MySQL installation directory, and look for the text "sql-mode"
Original Entry:
# Set the SQL mode to strict
sql-mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"
New Entry:
# Set the SQL mode to strict
sql-mode="NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"
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