Well, none of my issues have been fixed yet but MySQL support is on top of it.
I've ran into many S1 bugs: all at the same time. Support has been able to help me identify them. Some of them have proposed fixes, some fixes are being tested in
MySQL is by far the best Open source Database on the planet-support reflects that fact. I highly recommend getting a support contract to trouble shoot issues that make it into production, less learning the entire mysql code base and doing it yourself. (I know alot about the code-base but the 5 issues I am tracking was to much for me to debug alone. On top of that I don't know enough of the code base to make fixes to some of the bugs.)
If you do more then 30K selects per second across all your servers, get piece of mind that someone will do there best to address any issues that you can't figure out. Get a MySQL support contract today.