It would be easier to me to answer a few of the questions that has cropped up regarding Rhino.ETL.
Boo vs. Ruby: Why I choose to go with Boo rather than Ruby. Very simple reasoning, my familiarity with Boo. I can make Boo do a lot of stuff already, I would have to start from scratch on Ruby. I don't see any value in one over the other, frankly, is there a reason behind the preference?
NAnt ETL Tasks: The main problem I have with such an endeavor is that it is back to XML again, if I want to build complex processes, I want them to be easy to follow, and that exclude XML.
Active Warehouse: Interesting idea, but that is using the imperative approach, I want to do something a little more declarative, and I really want it to be on the .Net platform (hence, much more familiar & debuggable). I also in a position where I believe that it would actually take me less time to build the tool than learn a tool in a new language.
Other OSS ETL tools: There are quite a few OSS ETL tools that has been raised, they all share one problem from my perspective, they are not .Net and they are all visual / XML oriented.
I should also mention that I am building this project as preemptive step against the next project ETL's requirements, so I have both time to build it, and I have the craziest itch to scratch after dealing with SSIS in this project. The last time I was this excited about something, Rhino Mocks came out :-)