Sipke's lengthy session (he had a whopping 1,5 hours to fill!) about the APIs of Orchard and module development tips and best practices contained the wast majority of the techniques an Orchard developer needs to know about. Surely everybody in the audience could learn something new.
Piotr's session followed about localization, starting with clarifying the difference between localization and internationalization (for the solution you'd have to watch the session's video when it's available :-)), then following up with some best practices, basics of content and string localization, as well as with demoing the DbTranslations module.
The first day of the conference ended with the Panel, where the audience could ask Sébastien, Piotr, Sipke and Bertrand any question.