If you are using the XmlSerializer in your app, these pages might help you with some scalability problems:
Scott Hanselman's Computer Zen - Changing where XmlSerializer Outputs Temporary Assemblies
Scott Hanselman's Computer Zen - HOW TO Debug into a .NET XmlSerializer Generated Assembly http://www.hanselman.com/blog/HOWTODebugIntoANETXmlSerializerGeneratedAssembly.aspx
Also, make sure that you cache the XmlSerializer class that gets generated for your type. Each time a serializer class gets generated, it gets compiled into a separate assembly and loaded into your AppDomain. The problem is that assemblies can not be unloaded from an AppDomain so it just fills up with these generated assemblies.