As Monty, who is apparently working at MySQL, wrote yesterday in his blog, there appears to be a rahter large number of quite devastating bugs left in MySQL 5.1 at the time of its release, many of which would have been declared release critical by open source projects.
In Oops, we did it again, Monty names a number of these bugs and outlines variety of bad management decisions which have lead to the current situation, and which apparently have lead to similar situations in the past.
To me, it does not really come as a surprise. As you may or may not know, I have been following the MySQL company, community and products for years, and haven't seen too many different types of releases so far. In any case, I strongly support the suggestion of Monty and also strictly recommend staying with MySQL 5.0 for now &mash; or to migrate to PostgreSQL, if possible.