Keeping with the theme, here is a great introduction blog post from StructureMap creator Jeremy D Miller on Inversion of Control and Dependency Injection.
I have never used StructureMap on any live apps, which is a shame as i have followed its life cycle over the past few years as it documentation, mainly thru JDM's blog posts, have been very interesting. If you want to see how to integrate something like StructureMap into your existing code base check out Rob Conerys re factoring session with Jeremy . Actually check out the whole video series its great to watch as you get to see someone make mistake and fix them. People don't actually learn very well from watching experts, they learn better from watching people adapt after making small errors. wow.. 4 years of Pysch just paid off! so check it out and watch rob talk with Gods of .Net (JDM, Ayende etc)