I have learned many things at every PASS Summit I have attended. First off, all of the people who are speakers are just human beings like you and me (including everyone's favorite Kalen Delaney). I learned that it is really expensive to put on a conference like PASS, and I have especially learned to enjoy six dollar bagels and four dollar cans of coke, while they still exist. And I have learned that speaking in front of 200-2000 people isn't nearly as scary as it initially seemed. I have even learned many things about being a DBA\Database Architect that I might never have learned when I was just digging around books online.
However, the "best thing" I have learned is how to be a citizen of the SQL Server community. PASS, being a non-profit organization relies very heavily on people to donate their time. Up until this year (I am teaching a post-con with Paul Nielsen), I have never made one cent at the PASS Summit, and last year I spent over a thousand of my own dollars to attend. Why? Because I believe in the SQL Server community that PASS represents. During the time I have spent in the PASS community I have made lots of great friends, and I wouldn't trade any of them or even one moment I have spent at any Summit for anything.
I hope to meet you there this year adding to the community!