Any experiences with dependency injection frameworks? I am looking at StructureMap, Unity, and Spring.Net.

Also look at windsor it's part of the castle project

I decided to use StructureMap because it seemed the easiest to use (I did not want to fiddle with xml; I preferred to just put it in the code). So far its been great! Although I did abstract the whole thing so that I could swap out StructureMap for something else.