Unfortunately, late last week we discovered a nasty bug with load testing in VSTS 2008 SP1 that is a regression from the original RTM version of VSTS 2008: for Web test requests that result in redirects, any think time that is specifed on the request is ignored when the Web test is run in a load test.   Even more unfortunately, VSTS 2008 SP1 has been locked down for changes, so the fix for this problem will not make it in.  We will need to create a QFE to be applied to SP1 to fix the problem.  It takes some time to get through the QFE process.    In the meantime, it is possible to workaround this bug by adding a Web test plugin to each Web test used in a load test that uses redirects and think times (probably most Web tests).  The work around is to add the following WebTestPlugin to your test solution, and then add the Web test plug-in to each Web test (fortunately a Web test can have any number of plug-ins):

using Microsoft.VisualStudio.TestTools.WebTesting;

namespace TestProject1    // Change the name space as appropriate
{
    public class WebTestPlugin_FixThinkTime : WebTestPlugin
    {
        private WebTestRequest m_currentPageOriginalRequest;

        public override void PostRequest(object sender, PostRequestEventArgs e)
        {
            base.PostRequest(sender, e);

            if (!e.Request.IsRedirectFollow)
            {
                m_currentPageOriginalRequest = e.Request;
            }
            else
            {
                if (m_currentPageOriginalRequest.ThinkTime == 0 && e.Request.ThinkTime != 0)
                {
                    m_currentPageOriginalRequest.ThinkTime = e.Request.ThinkTime;
                }
            }
        }
    }
}

If you are already using VSTS 2008 SP1 Beta1, can you add this plug-in now to fix the existing bug, and the plug-in will still work when the final version of SP1 ships, and will not cause any harm once the QFE that fixes the bug is available (though it could be removed at that point).