Running a SSRS Stress Test with One User Account...Think Again! you are thinking about running a stress test against your Reporting Services 2008 environment, and you've setup your test harness (I'm biased to VS.NET Team Test 2008 with Load Agents) to use a single domain account.  When you run your stress notice an interesting error like this:

HTTP/1.1 503 There are currently too many requests in progress for user: "domain\username". Please wait until the current requests have finished processing before issuing any more.

So...what do you do?  Well, there's a parameter setting in the Reporting Services config files (MaxActiveReqForOneUser) that sets the number of concurrent reports that can be running at the same time for a single user...and by default its set to 20.  Simply increase the number to your desired setting.  See the SQL Server 2008 Reporting Services BOL for more info:

There's also a good post on this by John Gallardo: