FWIW, I've had periodic problems with slowness also, even when not many people are on the site. For me restarting the SQL server seems to fix it. Seems sometimes something in the SQL queries hangs and slows everything down. I've been trying for sometime to pinpoint what it is, but so far have not been able to. I even tried configuring MySQL to log slow queries, but that didn't show anything either. Last night for example, my users were complaining of a very slow forum, but this AM it's fast as lightening!