Did you find that you needed fewer after the upgrade? I'm in the middle of moving my 2.3.5 app to 3.0.3 and am finding that there are fewer plugins as some are now part of rails or made redundant; jrails and subdomain-fu come to mind.
I don't think we dropped a drastic number of plugins or gems. Probably a few, but then again we added a few as well to keep old features active as we transition out some deprecated Rails patterns.
I mentioned this in your Blog Comments but I thought I'd bring it up here. I mentioned that it would be interesting to see a portion of your QA spreadsheet you mentioned in your article.
Did you guys try to move to haml/sass from the existing view templates/stylesheets? Would like to know if you guys had good success rate moving to haml on a big existing project...
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.