Oracle has released another huge batch of improvements to MySQL slated for MySQL 5.6. The pace of innovation in MySQL is accelerating rapidly and the improvements are impressive. I have not read all of the blog posts thoroughly yet, but I’ve skimmed and it looks fantastic.
The link posted above is ONE of the sets of improvements: there are also a bunch of other posts about new improvements to the query optimizer, InnoDB, and probably more. But I don’t see a single table-of-contents blog post for those that I can link to. Hence I recommend that you look at Planet MySQL to find these posts.