Sergey Petrunia brought to my attention the work Optimizer Team has done in MySQL 6.0 related to SubQuery Optimization.
I am excited to see this information published honestly outlining the things which are fixed now and things which are still not handled well. According to the bug sampling done by Optimizer Team 68% of reported issues are fixed (significantly improved) by changes in MySQL 6.0 which is far from all the issues but still very good number.
If you had issues with subqueries in MySQL 4.1 or 5.0 and pulled away from using them I’d encourage you to try MySQL 6.0 and see if your issues are fixed or described in the documentation published. If not report the bug and let optimizer team to know how you’re suffering
Hopefully in the future we’ll see more MySQL teams being proactive with publishing results of their work and plans. I’m especially looking to see developers writing themselves rather than documentation team or marketing writing about new features as developers often able to go much more in depth and explain those boring details you can see omitted by professional writers.