A. Microsoft has released several documents outlining its scalability testing for the RTM version of SCSM 2010. A key one is "Hardware Performance", which talks about their tests of up to 50,000 users/computers in a single SCSM management group. Also, "Service Manager 2010 SP1 Deployment Scenarios" discusses SP1 sizing.
For more detailed sizing help, go to this page and download the job aids package. It includes numerous aids, such as Visio stencil objects for SCSM, architecture diagrams, and an Excel sizing spreadsheet to help you design your SCSM infrastructure based on your expected environment.