I have a few ideas about what a mid-level should know:  RAID, index tuning, virtual servers, load balancing, proper database design techniques (normal forms anyone?), security configuration and administration, T-SQL DDL and DML, the difference between declarative languages and imperative languages, maybe even some client connectivity info, etc.  If the mid-levels are teaching the juniors, then basically by mid-level it would seem they need to pretty much know it all