Thanks for taking the time to explain the internals of Rails3. Quick question, does the new ActiveModel API assume a relational database? I'm really hoping for a Rails compliant CouchRest implementation.
Excellent point about the 2008 change to the EPA's methodology. That was one of the first things that jumped out at me when I took the average of all makes and models by year. I was planning on writing a post about just that, but the link you provided to Edmunds explains it better than I could.
Also, great information about how the car companies can model their fuel efficiency during the design phase.
You are absolutely right, my data is probably more variable than yours, but I was surprised to see it go down as much as it did. I'd love it if you sent your data along, I'll write a post about it. I'm also planning on adding mileage tracking to the site for comparison to the EPA data. Some initial data would be great for bootstrapping.