David Shroyer published an interesting paper about a Different Approach to Implementing Time Calculations in SSAS. It is something I would have found the time to write since Analysis Services 2000 (I have being using a similar approach since then) and is a very good guide on the whole topic.
I completely agree that the Time Intelligence Wizard could generate a better MDX implementation. There are other consideration that can be made about Time Dimension and I hope to be able to write something about this in the next future… now that I found this good paper, I feel less pressure for doing that!