The learning curve was tremendous. Learning an older version of Rails, learning the monkeypatches on it, learning how to deal with metaprogramming from a refactoring perspective. Learning a new editor (SUblime, which I've grown to like quite a bit for dealing with really large files)
Learning about the team, and the team's customs (Jukebox for music was an interesting one...)
Environment issues, DNS server issues, lots and lots of Redis/resque issues.
Learning to take notes in a notebook rather than in evernote
Learning to take hipster jokes with grace and style- or at least without devolving into Godwin's law.
Reading innumerable books on the train.
Meetups- Ruby, Clojure, JavaScript, female developers (sorely needed), ChiSC (discontinued?)...
Setting up Bundler for a largish established app with custom local gems