Code Generation and the Open Close Principal
Vladan Strigo made a really inspiring comment about code generation in the NH Users list.
I didn't want to use codesmith for that because it would de-OCP-fy me in my future efforts :)
That makes a lot of sense, and manages to touch on what bothers me the most with code gen as an architectural approach. It gives up a very important concept, and that affect a lot of the stuff that is dependant on that.