What is the best methodology for building a .NET client application that supports plugins?

I found the .net plugin architeture architecture to be very difficult to use as a plugin framework. I think the plugin interface should be easy for 3 coders developing with.

Do you know / are using / etc some techinique plugin simpler and more efficient? To be more precise, imagine that we are developing a text editor such as notepad that needs (for example) plugins for different highlighiting syntax, interface changes, shell integration, etc.

Will you use the inline .net plugin code or will you create / use several different ones?