I recently finished a new article on Master Pages tips and tricks that covers different things you can do with Master Pages such as using the MasterType directive, working with base classes, and handling nested Master Page design issues in VS.NET 2005.  The article also discusses a technique published awhile back on my blog for sharing Master Pages across IIS applications.  The article is available on the Simple-Talk.com Website. 

Additional code covering different tips and tricks for Master Pages can be found here.