I wanted to provide a quick note on how to scale test Reporting Services.  Partially I'm posting this so I don't lose the link :-).

Often we are asked how best to scale test Reporting Services and what scale numbers to expect coming from a particular configuration.  We always hesitate to promise specific numbers because so much depends on your usage patterns, your reports, the size of your data, and your architecture.  To say that N users will always be supported by X hardware is just too much of a simplification.   Therefore the guidance we give is based on patterns we have seen in our testing lab.  You can see the guidance we gave for SQL Server 2005 Reporting Services here:

 http://www.microsoft.com/technet/prodtechnol/sql/2005/pspsqlrs.mspx

You should be aware that SQL Server 2008 CTPs (Community Technology Preview) are becoming available as 2007 continues.  To date, I believe we have provided 3 public SQL Server 2008 CTPs.  You can find the latest one here:

https://connect.microsoft.com/SQLServer/content/content.aspx?ContentID=5395

As always with a new version, users want to know how well it scales relative to the old version. Bear in mind that these CTPs are kind of like Alpha or Beta releases of the product - they're not finished yet and performance/scale characteristics will change as we get closer to release. 

However, if you're thinking of adopting the next version, now is the time to start planning your testing strategy.  Specifically, you can start by building your test infrastructure to do scale testing against the existing product and reuse as new CTPs come available.  The leg work to understand which reports are key to test and which scenarios you should be including is independent of your actual testing timeframes and having it done and out of the way can greatly simplify your acceptance testing later.  In this regard, you may find the following article very interesting (I did):

Using Visual Studio 2005 to Perform Load Testing on a SQL Server 2005 Reporting Services Report Server (http://technet.microsoft.com/en-us/library/aa964139.aspx)

Whether you go with this approach or another solution, you will be well served to start planning this testing well in advance of having the final product in place.  Also, we have not released any guidance on perf/scale for SQL Server 2008 Reporting Services; this will come in due course as we get closer to release.

Take care and good luck,

-Lukasz