Kevin Holman has already published the SCOM SQL bible - http://blogs.technet.com/b/kevinholman/archive/2007/10/18/useful-operations-manager-2007-sql-queries.aspx but I've one update.
When trying to see where your performance data is, I've added a "rule" column to one of Kevin's queries making it easier to track down and override those data hogs!
select top 20 pcv.ObjectName, pcv.CounterName, r.RuleName, count (pcv.countername) as Total
from performancedataallview as pdv, performancecounterview as pcv, rules as r
where (pdv.performancesourceinternalid = pcv.performancesourceinternalid) and (r.RuleId = pcv.ruleid)
group by pcv.objectname, pcv.countername, r.rulename
order by count (pcv.countername) desc