MySQL 5.6 on OS X 10.8.2 disconnects on user creation?
Alright another instance of "read your damn logs" :)

tail /usr/local/var/mysql/username.local.err told me:

2013-02-25 11:29:50 1616 [ERROR] Native table 'performance_schema'.'accounts' has the wrong structure
2013-02-25 11:29:50 1616 [ERROR] Native table 'performance_schema'.'hosts' has the wrong structure
2013-02-25 11:29:50 1616 [ERROR] Native table 'performance_schema'.'socket_instances' has the wrong structure
2013-02-25 11:29:50 1616 [ERROR] Native table 'performance_schema'.'socket_summary_by_instance' has the wrong structure
...


So a quick google turned up the answer: sudo mysql_upgrade -u root -ppass