MySQL VARCHAR Performance

1. http://stackoverflow.com/questions/332300/is-there-a-real-performance-difference-between-int-and-varchar-primary-keys
2. http://nicj.net/2011/01/20/mysql-text-vs-varchar-performance
3. http://www.mysqlperformanceblog.com/2008/01/24/enum-fields-vs-varchar-vs-int-joined-table-what-is-faster/