Upon trying a
rake generate task, I saw errors in the Ruby gems for processing YAML. I assume this is due to the fact that I built them on the older OS X install.
Interestingly, RVM survived the upgrade and seems to be working just fine.
I followed the instructions here to uninstall and reinstall Ruby, the bundler, and all bundled gems for my octopress install. The instructions mention a specific problem for OS X Lion, but these steps solved the problem for me.