Did some performance testing of our website using Microsoft's Web Application Stress tool. It's a pretty nice gizmo, and I higly recommend it. It will let you interactivly record a web browsing session, and let you play it back. It records all the headers, cookies, everything. It will also let you load a (IIS) log file, and play that as a session. It has options for the number of similtanous sessions, etc (it's free, too).
I'm creating a version of our web application to get data from a proprietry backend system, via COM/MTS objects to our Java Servlet/JSP website and application server, instead of just hitting a database.
I'm pretty happy - it seems pretty much as fast as the database version at the moment, from what I can tell.