I attended FOSDEM this year. As always, it was very busy, and the Brussels transport system was as confusing as ever. This time it was nice to accidentally bump into so many people I know from years past.
Lunar's talk on reproducible builds of Debian packages was interesting - being able to independently verify that a particular binary package was built from a particular source package is quite attractive.
Also Mailpile declared an alpha release. The bit in the talk that I didn't know already was the description of exactly how the search function works. Seeing how they integrate GPG into the contacts/compose features brought home how lacking most (all?) other mail clients are when it comes to usable encryption.
On Sunday afternoon I managed to grab a seat in the Go devroom, to hear about crazy things like how YouTube are putting a daemon called Vitess in front of MySQL to abstract away sharding (at the cost of some transaction guarantees). You would have thought Google would already have a scalable data store of some sort?
Other bits I remember: Michael Meeks talking about GPU-enabling spreadsheet formulae calculations. And hearing Wietse Venema talk about Postfix was pretty awesome.