Jamroom is really only limited by the hardware platform you put Jamroom on, the number of Artist Profiles your Jamroom install is licensed for, as well as the amount of bandwidth available to it for streaming media files. There are Jamroom Sites that are hosting well over 50,000 profiles on a single server.
Jamroom makes extensive use of a MySQL database, so as you grow larger one of the things to keep an eye on is your MySQL resource usage - you may end up needing to increase the number of available MySQL connections. If you get errors from Jamroom that it is unable to connect to the database, this could be the problem. See the MySQL Too Many Connections document for more information.
Also, if you are using the “Jamroom Lofi Creator”, a fast processor is recommended if you are running a large system (or an upgrade to a Jamroom Cluster Server), since the conversion time can take a while. The faster the processor, the shorter the amount of time for conversion, and the less likely it will be that your system will slow down at all. It typically takes about 30 seconds to create a LOFI Audio File from a 6 Megabyte HIFI Audio File on a Pentium 4 2.4Ghz machine.
If you are interested in running a very large (50,000+ profiles) Jamroom, make sure and check out the Jamroom Cluster Server. The Jamroom Cluster Server allows you to grow your Jamroom without worries about limits on your hardware, bandwidth, or profiles, as it will scale and grow with you as your Jamroom grows. The Jamroom Cluster Server can be purchased online via the Jamroom Store.