As per Oracle’s press release
In recent benchmarks using the release candidate for MySQL 5.5, compared to MySQL 5.1, results demonstrated marked performance improvements:
On Windows: up to 1,500 percent performance gains for Read/Write operations, and up to 500 percent gain for Read Only(1).
On Linux: up to 360 percent performance gain in Read/Write operations and up to 200 percent improvement in Read Only(2).
Lets hope these numbers live up. Many of the users are not that excited about it. One of the main concerns being this Oracle’s first MySQL release.