Licensing models can sometimes make database modeling seem trivial. Per processor or per seat? Single core, dual-core, multi-core processors? Multiple instances on one server? Virtualizing servers on a single server? It can get very confusing, very quickly.
Recently, I was asked by a former student about licensing for a SQL Server Reporting Services instance. In the proposed scenario, the Report Server would be installed on one server and the back end database would be installed on a separate, remote server. How many licenses of SQL Server are required?
In short, each server where a Business Intelligence component is installed requires a valid SQL Server license. So, a remote database deployment scenario where the Report Server is installed on one server and the ReportServer database is installed on a separate server requires two licenses of SQL Server.
But don't take my word for it. Here are a couple of links that will help clarify licensing requirements.
Special Licensing Considerations for SQL Server 2005
SQL Server 2008 Pricing and Licensing
Cheers and I hope this helps!