The first beta release of MySQL 5 is now available. If past experience is anything to go by, an alpha version will follow, and then the first production release will follow that. Due to the nature of the software, it will go through a few more months of testing before it will be considered production safe by the MySQL people. Looks like a big step forward for the database!
Updated 2021 : note that the above post is out-of-date, given this post was originally published in 2005, but is left here for archival purposes.