.NET class libraries

I come from a J2EE background and am having trouble finding good material on best practices for building and storing reusable middle tier classes in .NET.

I have touched upon Assemblies and Strong Naming and the GAC, but have yet to find an elegant design pattern analogous to building packages of utility/business/data access/etc classes to be used throughout the enterprise as in J2EE.

MS doesn't even seem to have much literature on the subject, and few people I talk to have attempted to do this, for reasons I can?t fathom. Why is that?

Does anyone have any suggestions and/or documentation on how to accomplish this?