Hidden gems in 5.1
* Prepared statements can now use the query cache. BUG #735
* InnoDB auto_increment insertion is more scalable. Manual Page
* The long_query_time can be set to values less than 1 second. BUG #6238
* SHOW PROFILES is available for everyone, not just community users!
* Creating Triggers no longer requires the SUPER privilege.
Let's hope for 1000 more of these in MySQL 5.4.