On the hack day I did a presentation about how to contribute to WordPress Core. Since it was an ad hoc thing, I just borrowed Andrew Nacin’s slides. :-)
Besides the being-in-Lisbon (which is fantastic) and the after-parties, the hack day was the big win for me. I geeked out with Bruno Carreço, a colleague from AppThemes. Also, I participated in a productive discussion about how to properly implement a plugin for multilingual sites; I hope Remkus sees it through.
Ignoring the two missed flights, it was a great experience!