Who would want to miss a keynote titled Beefy Web App seeks Sexy AJAX stunner for interface fun and maybe more?
And if that doesn't convince you, you can opt for the more wholesome versions of Browser Technology, Core Technology or Open data, or various tutorials depending on which flavors of X.* languages your preferences lay.
related items:
xtech06.usefulinc.com/
upcoming.org/event/34103/
barcamp.org/BarCampAmsterdamII