Unlike Shopify, we did not start during the beta days. Certainly we were aware of what was going on and experimented, but our Rails3 branch didn't exist since the spring or anything.

Looking through our git logs, I believe early September is when we really started to look at Rails 3 in earnest. We landed the branch in the second week of November. The code work was a solid month plus, and we spent nearly as much calendar time, and probably more actual person-hours, in testing and fixing thereafter.