Lots of articles out there (see Slava Oks's original SQL 2000 article and Kevin Kline's SQL 2005 update) recommend disabling hyperthreading on SQL servers, or at least testing your specific workload before enabling it on your servers.
This issue is gradually becoming less relevant as true multi-core processors replace hyperthreaded ones, but what's the current wisdom on this issue? Does this advice change any with SQL 2005 64-bit, or SQL 2008, or Windows Server 2008?
Ideally, this should be tested in advance in a staging environment, but what about for servers that have already made it into production with HT enabled? How can I tell if performance issues we're experiencing might be related to HT? Is there some specific combination of perfmon counters that might point me in that direction, as opposed to all the other things I normally pursue when working on improving SQL performance?
Edit: This is especially attractive because of the potential for an across the board improvement for some of my high-cpu servers, but the client is going to want to see something concrete that helps me identify which servers really could benefit from disabling hyperthreading. Of course, conventional performance troubleshooting is ongoing, but sometimes any little bit helps.