MySQL Backend Support

This would also be useful for those who have existing MySQL systems and would like to integrate the DAViCal back-end data easily with those, especially if they don't have an events/calendaring system already.
 * Definitely concur. I haven't looked at the code but reasonably portable database code should be feasible. For sites that already use a DBMS having to install, configure and most importantly support a new one is a major barrier to entry.
 * Feel free to scratch your itch :-)

Database Access Layer
Currently DAViCal uses a database layer which was written by Andrew McMillan over the last six years or so, and which is PostgreSQL specific. With the advent of PDO and PHP5 this could be rewritten to use PDO which would be an ideal first step in arranging for database independence. Andrew is happy to receive patchs which implement the core functionality of the PgQuery library using PDO, and very likely to do it himself when PHP4 is dead enough to ignore.

PdoQuery
Some design work has now started on the replacement library which will be PDO based, and will allow some hooks for different database dialects. See the PDOQuery page for full details.