PLDI was a great experience for me this year. The location was great -- it's not often you get a chance to visit one of the most historic cities in the world (and meet CS people from all over the world!). Aside from the great things I saw in Beijing itself, a few things stuck with me.
Aaron Turon's work with "reagents" is pretty cool. As a person who does a lot of parallel programming, I know how difficult it can be to write synchronization code. Reagents allow you to express complex synchronization patterns in a way that's concise and understandable -- many of the canonical examples (used in textbooks, for example) can be clearly written using reagents in a way that is much closer to a plain-English description of how they're supposed to work. The great part about them is that not only are they easy to use, but they can also give you performance that's competitive with hand-tuned libraries (e.g. java.util.concurrent). Very nice work.
I also wanted to note that my experience student-volunteering was much better than I anticipated. I admit I didn't expect to get anything more out of the conference as a volunteer than I would as a regular attendee, but I ended up working in a session with a very small number of people. This actually turned into a great networking opportunity for me -- and the people there even asked me to stand up at the end of the session and demo my own work. You never know when you'll be given a chance to show your stuff to others in the community!