Common wisdom with previous generations of server hardware was that SQL Server might not benefit from hyperthreading or could be degraded at high CPU usage; does anyone have definitive data about Nehalem (non-EX) servers and SQL Server 2005 or 2008?
Here are some resources:
http://support.microsoft.com/kb/322385
http://sqlblog.com/blogs/kevin_kline/archive/2007/08/18/the-perils-of-hyperthreading-for-sql-server.aspx
http://blogs.msdn.com/slavao/archive/2005/11/12/492119.aspx
http://technet.microsoft.com/en-us/magazine/2007.10.sqlcpu.aspx
http://serverfault.com/questions/33515/current-wisdom-on-sql-server-and-hyperthreading
I am wondering whether Nehalem changes this story at all.
[Follow up 2/12/2010: I tested, and did some further reading, and decided to split the difference on this: transactional systems that have high numbers of connections and small queries have HT enabled, and our reporting/warehouse system that does fewer but more complex queries has it turned off.]