It's an MVC app, although business logic will be in business objects, so it will be something like MVC -> Business Objects -> Entity Framework. Theoretically, the business object layer will work with any type of .NET front end. My main concern is the ability to put a customized business object in a separate DLL.

>That's one pupose of IoC. But there may be other ways. Is this an ASP.Net or MVC app?
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>>In our vertical market VFP app, we use a data-driven abstract factory to instantiate all of our classes containing business logic. Basically, that means instead of using CreateObject("MyClass"), we use Factory("MyClassKey"). The factory looks up the class in a table, then instantiates and returns the object. An important benefit of the factory is that it allows us to substitute a custom class for the standard one. For example, if a client wants us to customize a calculation for them, we put it in a custom class, install it on their system, then use the factory to instantiate the custom class in place of the standard one.
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>>I'm wanting to implement something similar in C#. The customizations for a specific client would be compiled into a custom DLL. Then I need to instantiate the custom class in place of the standard one. I figure I could probably roll my own factory using reflection and whatnot. I wondered if there was already a standard solution to this problem. I've been learning about IoC containers, but I can't tell if they do what I need. I'm not sure I buy into all of the dependency injection stuff, but I would be willing to use an IoC container if it also met my need with customizations. Or maybe there is some other mechanism built into .NET to achieve what I need. Any suggestions?