I have done some recent work on MySQL. Most of my work on the database side pertains to MS SQL Server, Oracle and DB2 but at times, I have done some MySQL related work as well. Here are some good links on MySQL:

• MySQL white papers: http://www.mysql.com/it-resources/white-papers/
• MySQL case studies (yahoo, Cox Communications, AP, etc.): http://www.mysql.com/it-resources/case-studies/
• MaxDB information: http://www.mysql.com/products/maxdb/
  (MaxDB is an enhanced SAP DB, with cursors, stored procedures, triggers, views, etc.) … see http://dev.mysql.com/downloads/maxdb/7.5.00.html
• Database comparison tool: http://dev.mysql.com/tech-resources/features.html (compare against SQL Server, Oracle, postgres, etc.)
• MySQL Reference Manual: http://dev.mysql.com/doc/mysql/en/
• The main dead tree reference guide would probably be High Performance MySQL. There’s a list of others at http://dev.mysql.com/books/